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[ Silence ]

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>> Alright, this is CS50,
the start of week 9.

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So we've got a great week of
stuff in store for you more

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on web, more on database,

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more on actually looking
toward the final project

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but first, the blink tag.

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So this is a tag in HTML that
has been largely deprecated,

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which means the world
hated it and ripped it

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out of more recent
versions of HTML.

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But this week, well,
we teach you by way

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of a language called JavaScript

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to re-implement this
incredibly annoying feature

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of websites 1990 style.

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But our other teaser
for today is this.

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So, thanks to our
friends at Microsoft,

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they have a brilliantly named
research and development center

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in Kendall Square called NERD

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or New England Research
and Development.

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It's a beautiful space,
overlooks the Charles River.

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They've got a huge
digital screen

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and they're gonna
have a lot of pizza

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and candy waiting
for us this Friday.

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So the first ever CS50 movie
night will be this Friday.

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If you would like to RSVP
for this and join us, friends

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and family and dates
and such are welcome.

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Just go to cs50.net/movie,

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it's where everyone will
be this Friday night.

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And what we will do is CS50
now operates its own shuttle

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services, so thanks

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to Shuttleboy shuttle
services will be shuttling us

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over from Harvard Square
to Kendall and back.

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Event itself is at 7:30
and the movie that will be

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on the screen is this
year's course favorite.

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So, for those unfamiliar,
a little teaser trailer.

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[ Pause ]

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[ Noise ]

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[ Background Noise ]

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>> From Mike Judge creator
of Beavis and Butt-head

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and co-creator of King
of the Hill comes a movie

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about people who go to work.

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[ Noise ]

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>> Who are part of a team.

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>> And remember next Friday
is Hawaiian shirt day.

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>> Okay, if it-- I could
take the building on fire.

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>> Who respect their boss.

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>> We need to talk
about your flare.

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>> Well, I have 15--
15 pieces on.

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>> 15 is the minimum.

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Brian for example has 37
pieces of flare out there.

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[ Laughter ]

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>> And a terrific smile.

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>> And need to escape.

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>> I don't like my job

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and I don't think I'm
gonna go any more.

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>> One of these days I-- I
just kicked this piece of-

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>> I'm thinking now it might
be more fun to just get fired.

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>> And I've always wondered
what that would take.

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>> Oh here, listen.

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>> It looks like you've
been missing quite a bit

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of work lately.

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>> Well, I wouldn't say
I've been missing it, Bob.

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[ Laughter ]

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>> That's just a
straight shooter

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with upper management
written all over him.

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>> We're gonna be getting
rid of these people here,

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Mr. Samir [inaudible].

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[ Inaudible Remark ]

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>> Not gonna work
here anymore anyway.

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>> You haven't even shown up
and you get to keep your job.

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>> Actually I'm being promoted.

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>> Thank you, Bob.

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>> This is a-- a suck.

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>> They're gonna throw
you out on the street

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so that Bill Lumbergh
stock will go up.

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>> Oh, it's completely unfair.

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Initech deserves to go down.

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We're just the guys to do it.

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Tell me about that virus
you're always talking about,

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the one that could rip off the
company for a bunch of money.

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>> I'm not going to
do anything illegal.

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>> Illegal?

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Samir, this is America.

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[ Music ]

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>> The worst they're
gonna do is they put you

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in a white collar
minimum security resort

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for a couple of months.

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Do you know they have
conjugal visits there?

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>> I might be showing
her my oh face.

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Oh, oh--

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>> They let you have
sex with women?

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>> They sure do.

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>> Okay, I'll do it.

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[ Background Music ]

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>> Office Space.

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>> I know how you're getting
pretty depressed about your job

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and everything and so I
just want to tell you,

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good things can happen
in this world.

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I mean look at me.

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[ Laughter ]

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[ Music ]

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>> So coming this
Friday to CS50.

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So if you think you can
go, do RSVP by the website.

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Space will be limited
but we will follow

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up via email once we
know the logistics.

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So also coming up,
our CS50 seminars,

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this is a tradition we've
had for several years

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where the teaching fellows
and course assistants

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and Harvard affiliates
offer some hands on

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or conceptual seminars
on material bits.

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Either just of technical
interest to folks

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on campus specifically CS50
students or also on topics

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that might be of interest
to you for final projects

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so that you can pick
up some new skill

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or leverage some
new understanding.

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This year's line up includes
such titles as these,

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Blackberry application
development or crash course

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in Java, creating awesome
websites with Ruby on Rails,

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which is another programming
language and framework .

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Developing apps for
iPhone, iPod Touch and iPad,

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educational software
developments

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and Linux demystified, if
you're still a little mystified.

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Making SMS mobile applications,

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modern client side
web programming,

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socializing your apps with
the Facebook platform VIM,

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and then we have
dozens of past seminars

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and videos thereof
on this website here.

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So if you go to
cs50.net/seminars, you can one,

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see those videos and two,
RSVP for this year's lineup.

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Essentially all of these
seminars are in the process

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of being scheduled now.

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They'll be like an hour or two
some time, ideally between now

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and Thanksgiving, and the
seminar leader will follow

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up with you once you've
RSVP'd for it to figure

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out what might be an
optimal day and time.

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And rest assured if you can't
make this seminar's day time

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this year, it too will be
videotaped and put online

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within a couple of days
thereafter, so plenty of time

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to pick up some new skills
for the final project.

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And just to plant this reminder,

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the final project's pre-proposal
is due this coming Monday.

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This is a very casual but
very much expected email

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to your teaching
fellow just to let him

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or her know what you're
thinking, to bounce ideas off

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of them and to perhaps
have a little sanity check

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as to whether what you're
thinking is too easy, too hard,

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too much time, too little time,
it's really just an opportunity

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to get the juices flowing.

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And then in a couple of weeks
will the actual proposal be due.

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Also coming up from the
IOP, if you would like today

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in Mather House at 5 p.m.,
you can met Alec Ross

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who is the current
senior innovation adviser

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to Hillary Clinton where he
leads the state department's

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efforts to find practical
technology solutions for some

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of the globe's most vexing
problems on healthcare, poverty,

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human rights and
ethnic conflicts.

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So if you're interested
in how technology

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and social networking tools
can be used in diplomacy

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and social development,
do check out this event

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in Mather House this afternoon.

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So, my teaching fellows
and CA's and some

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of your classmates had a little
Halloween party yesterday

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and I couldn't help but delight
in the geekery of the jokes

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that get tossed around
at such events like this.

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So the risk of embarrassing
one of them anonymously,

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we heard this line here during
the preparation of the event

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where some balloons
were being hung

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and some Halloween
decorations were being hung.

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This volunteer simply
asked this here.

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And his friend's answer, his
or her friend's answer was--

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[laughter] That's sad, we all
laugh now 'cause we all get it

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for better or for worse.

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So, that was a cute thing to
see certainly for a teacher.

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So, I got this spam
actually this morning.

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Some of you probably did too.

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Hopefully none of you
actually clicked the link

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that you were given.

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This is from Harvard
University, it was sent to me,

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a dear web mail user and they
explained that due to congestion

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in all Harvard University
exclamation point,

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web mail users' accounts,
Harvard University,

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would be shutting down some
unused web mail account.

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In order to avoid
the deactivation

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of your web mail account, you
will have to confirm in a--

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confirm that it is a
present used account

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by clicking the secure
link, all caps below.

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The personal information
requested is

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for the safety of your accounts.

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Please leave all
information requested,

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then you can click here and go

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to what's clearly
harvard.edu/secure/login,

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which makes it secure,
and this is

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of course copyright
the president

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and the fellows of
Harvard College.

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So the thing is if you actually
clicked through that link,

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you actually end up on
this to your website.

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Too bad I clicked too
late because whoever had--

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you signed up for this
account has been deactivated.

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But we probably would have
seen a little web based form

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with text fields
and a submit button.

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One of which probably would
have said my user name.

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One of which would have said
my password and, you know,

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we kind of maybe smile now or
maybe you're a little worried

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that you did fill out a
form at 123contactform.com.

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But it really is
easy to do this.

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I mean this is what's generally
known as a fishing attack

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where the adversary is
essentially trying to bait you

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into doing something that sounds
legitimate technologically

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or socially, and it looks like
this is a harvard.edu link.

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So surely it must
actually lead there.

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But of course as we've already
realized a week ago in looking

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at HTML, all it takes to
make a link in a web page is

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to say A HREF equals quote
unquote HTTP slash slash.

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And then I could go
to 123contacform.com

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and then some other stuff.

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But then I can close this tag,

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but recall that what goes inside
this tag is the actual text

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that the user sees.

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So some websites would just
say something like click here,

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some websites would say
something like form,

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but some websites could
very well just say

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http://harvard.edu/secure/login
and voila,

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you have this duality.

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The link says one thing but
actually goes somewhere else.

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So if you're not sort
of savvy when it comes

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to detecting these
things now, you know,

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most any email clients, you can
hover your mouse over a link

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like that and actually see
where it actually leads.

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You can click it but at
least after you graduate

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from this course, stop
short of actually filling

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out the form and
clicking submit.

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At that point, you've
indeed gone too far.

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But it all boils
down to the basics

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that we've started
looking at today.

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So, where are we
going with this?

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Well, problem set 7, which
some of you have dived

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into is on CS50 finance.

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This is your first of two web
based programming challenges

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whereby you'll implement
an e-trade like website,

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whereby thanks to Yahoo
Finance, you'll be able

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to have users login or
register for accounts.

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>> They'll be handed some
10,000 virtual dollars

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and then you can actually get
nearly realtime stock quotes

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by typing in the stock
symbol for a company.

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You can "buy" the stock from
your 10,000 dollars in cash

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by checking with
the current prices

246
00:10:20,156 --> 00:10:21,726
and then buying those
numbers of shares.

247
00:10:21,726 --> 00:10:23,276
And then the code you will write

248
00:10:23,276 --> 00:10:25,816
for this problem set will
actually keep track of all

249
00:10:25,816 --> 00:10:28,356
of these transactions, all of
the buys, all of the sales,

250
00:10:28,356 --> 00:10:29,836
the sell point, the buy point,

251
00:10:29,836 --> 00:10:33,406
the prices at which you actually
transacted these changes.

252
00:10:33,406 --> 00:10:37,026
And all of this will be logged
in what's called a SQL database

253
00:10:37,026 --> 00:10:39,116
which is what we'll now
introduce as a mechanism

254
00:10:39,116 --> 00:10:42,796
for actually storing data
around on disk or in memory

255
00:10:42,796 --> 00:10:44,756
so that the next time the
user visits this page,

256
00:10:45,016 --> 00:10:48,736
they can actually interact with
it seeing their own profile.

257
00:10:48,736 --> 00:10:52,036
So if I go actually
to cs50.net/finance,

258
00:10:52,256 --> 00:10:54,326
you'll see the stacks
implementation of this.

259
00:10:54,396 --> 00:10:56,066
And if you actually
follow the link here

260
00:10:56,066 --> 00:10:58,446
that says play the big
board, you'll actually log

261
00:10:58,446 --> 00:11:01,516
in as your self, not as
some fake testing account.

262
00:11:01,656 --> 00:11:04,656
And if you do that and
then follow up through

263
00:11:04,786 --> 00:11:09,546
to the big board for problem
set 7, you'll see that all

264
00:11:09,546 --> 00:11:12,556
of us have lost at least 1
percent of our 10,000 dollars,

265
00:11:12,556 --> 00:11:13,896
those of us who opted
in to this here.

266
00:11:14,146 --> 00:11:16,986
So much like P set 6 had its own
big board similarly will this

267
00:11:16,986 --> 00:11:18,546
one just for fun have
its own big board.

268
00:11:18,846 --> 00:11:20,156
And now that I look at this,

269
00:11:20,246 --> 00:11:23,256
the mathematics are clearly off
'cause Michael Shan [phonetic]

270
00:11:23,256 --> 00:11:27,866
is-- has up to 32,000 dollars
but he's only up 2 percent

271
00:11:27,866 --> 00:11:28,656
and he's ranked the last.

272
00:11:28,856 --> 00:11:31,426
So this is an example
of a bug at the moment.

273
00:11:33,106 --> 00:11:35,576
In my defense, the markets
were closed this weekend

274
00:11:35,576 --> 00:11:36,456
when I was testing.

275
00:11:36,456 --> 00:11:38,026
So I couldn't really
get real data

276
00:11:38,026 --> 00:11:39,246
but this is clearly my fault.

277
00:11:39,286 --> 00:11:40,446
So I will fix.

278
00:11:40,446 --> 00:11:44,366
But as it has it, David J.
Malan is actually number 1

279
00:11:44,366 --> 00:11:45,156
at the moment, so--

280
00:11:45,156 --> 00:11:45,223
[ Laughter ]

281
00:11:45,223 --> 00:11:48,526
>> -- maybe I should
leave it alone.

282
00:11:48,666 --> 00:11:50,636
So, what's really
cool about this is

283
00:11:50,636 --> 00:11:53,206
that this project
originated really just as kind

284
00:11:53,206 --> 00:11:56,356
of a random idea where we
wanted to do something related

285
00:11:56,416 --> 00:11:58,286
to finance but to do this well,

286
00:11:58,526 --> 00:12:01,056
you really wanna get some
kind of real data ideally.

287
00:12:01,056 --> 00:12:02,916
'Cause if we just handed
you a big Excel file

288
00:12:02,916 --> 00:12:05,186
and said here are the prices
of all these company's stocks

289
00:12:05,556 --> 00:12:08,286
on October 1st, 2010, I
mean who cares, right?

290
00:12:08,286 --> 00:12:10,306
You could use that data,
much more interesting

291
00:12:10,306 --> 00:12:12,316
to interact with it in realtime.

292
00:12:12,586 --> 00:12:14,816
So if I do a look
up for a company

293
00:12:15,016 --> 00:12:18,616
like Google whose symbol
is GOOG, what you'll get

294
00:12:18,616 --> 00:12:20,796
on Yahoo Finance really,
any of these websites

295
00:12:20,796 --> 00:12:23,026
that give you free stock
information are details

296
00:12:23,026 --> 00:12:24,386
like the last trade price,

297
00:12:24,386 --> 00:12:26,696
Google currently
goes for 614 dollars.

298
00:12:26,946 --> 00:12:29,326
When the last trade was
transacted, what the bid

299
00:12:29,326 --> 00:12:30,456
and asking prices are.

300
00:12:30,636 --> 00:12:32,006
If you're not familiar
with some of this jargon,

301
00:12:32,006 --> 00:12:33,996
it's not really a big deal
for the P set but we link

302
00:12:33,996 --> 00:12:36,046
to a nice tutorial
and the PDF this week

303
00:12:36,046 --> 00:12:37,396
that will bring you
up to speed on this.

304
00:12:37,736 --> 00:12:39,446
But what caught our eye is

305
00:12:39,446 --> 00:12:42,296
that there's all these
interesting data on the page

306
00:12:42,526 --> 00:12:43,846
and we could resort

307
00:12:43,846 --> 00:12:45,976
to a technique called
screen scraping.

308
00:12:45,976 --> 00:12:48,976
Screen scraping or web
scrapping is just the buzz word

309
00:12:48,976 --> 00:12:53,116
that describes writing a program
usually in a language like PHP

310
00:12:53,116 --> 00:12:55,856
or in Ruby or in Python,

311
00:12:55,856 --> 00:12:57,526
something called a
scripting language

312
00:12:57,526 --> 00:12:59,266
which we'll revisit
today and onward.

313
00:12:59,856 --> 00:13:03,756
That is whose purpose in life
is to pretend to be a browser,

314
00:13:04,016 --> 00:13:07,346
make an HTTP request, and this
is just a program you could run

315
00:13:07,346 --> 00:13:08,866
at the command line,
on the cloud,

316
00:13:08,866 --> 00:13:10,146
on your own computer, wherever.

317
00:13:10,146 --> 00:13:10,906
It can be written in any

318
00:13:10,906 --> 00:13:12,676
of these new languages
we're starting to play with.

319
00:13:13,056 --> 00:13:15,716
It makes HTTP request
to yahoo.com

320
00:13:15,976 --> 00:13:18,076
as though it's a browser,
and that's not all

321
00:13:18,076 --> 00:13:20,826
that hard 'cause we sniffed my
own traffic last week and saw

322
00:13:20,826 --> 00:13:23,626
that when you make an HTTP
request, this just sends some

323
00:13:23,626 --> 00:13:27,676
of these HTTP headers, host
colon and GET and then dot, dot,

324
00:13:27,676 --> 00:13:30,196
dot and so you can mimic
that stuff very easily

325
00:13:30,196 --> 00:13:32,046
with a few print
calls in a program.

326
00:13:32,316 --> 00:13:35,606
So we could pretend to be
a browser, get this page,

327
00:13:35,756 --> 00:13:39,786
specifically this URL, because
notice what's nice here is Yahoo

328
00:13:39,786 --> 00:13:42,116
apparently is using
the GET mechanism

329
00:13:42,286 --> 00:13:45,096
which means you can parameterize
requests of a web page

330
00:13:45,336 --> 00:13:48,066
by using a HTTP parameter.

331
00:13:48,066 --> 00:13:50,336
In this case, notice
that the URL starts

332
00:13:50,336 --> 00:13:53,796
with finance.yahoo.com/q,
probably for query,

333
00:13:54,036 --> 00:13:57,036
question mark, and the question
mark means here comes some

334
00:13:57,216 --> 00:14:00,636
parameters, here comes
some inputs to this server

335
00:14:00,876 --> 00:14:03,636
and the first input is
called S, that's a parameter

336
00:14:03,856 --> 00:14:07,086
and its value is
apparently equal to GOOG.

337
00:14:07,376 --> 00:14:09,676
So what this means is I
could literally copy this,

338
00:14:09,966 --> 00:14:13,956
paste this URL into my own
PHP program and write code

339
00:14:13,956 --> 00:14:15,536
that says go get that URL.

340
00:14:15,536 --> 00:14:18,786
And I can say go get that URL
every minute or every hour.

341
00:14:19,026 --> 00:14:21,616
I can use something as an
aside called the cron job

342
00:14:21,776 --> 00:14:23,626
which actually automates
the process

343
00:14:23,626 --> 00:14:25,026
of running your code
on a schedule.

344
00:14:25,246 --> 00:14:26,826
So with all these
little building blocks,

345
00:14:26,876 --> 00:14:30,726
something like PHP, something
like a so called cron job,

346
00:14:30,726 --> 00:14:33,246
I can actually grab this
data again and again.

347
00:14:33,606 --> 00:14:37,006
But unfortunately, even
though it looks obvious to me,

348
00:14:37,006 --> 00:14:39,666
the human, that the number I
probably want the most is this,

349
00:14:39,666 --> 00:14:40,816
the last trade time.

350
00:14:41,016 --> 00:14:43,146
Or you know what, maybe
it'd be interesting

351
00:14:43,146 --> 00:14:44,986
to get the current change.

352
00:14:44,986 --> 00:14:46,156
Maybe it'd be interesting

353
00:14:46,156 --> 00:14:48,726
to get the current opening
price or the bid part.

354
00:14:48,906 --> 00:14:50,806
In other words, there might
be a lot of pieces of data

355
00:14:50,806 --> 00:14:53,056
on the screen and so those of--

356
00:14:53,056 --> 00:14:54,466
those people in this world

357
00:14:54,466 --> 00:14:56,226
without a computer
science background

358
00:14:56,226 --> 00:14:59,146
or any programming jobs
probably would open up Excel

359
00:14:59,146 --> 00:15:01,536
or Google spreadsheet and then
just start transcribing these

360
00:15:01,536 --> 00:15:03,276
numbers manually,
right, copy and paste.

361
00:15:03,276 --> 00:15:04,846
And that's about as
efficient as you could get.

362
00:15:05,336 --> 00:15:09,476
But remember that underneath
the hood here is some HTML.

363
00:15:09,626 --> 00:15:12,716
So if I actually go and view
the source of this page,

364
00:15:13,196 --> 00:15:14,996
let's do it this
way, view source,

365
00:15:15,226 --> 00:15:16,706
I'll see all of these HTML.

366
00:15:16,706 --> 00:15:21,286
But my God, now finding those
little needles in this mess

367
00:15:21,286 --> 00:15:23,426
of a haystack is really
quite challenging.

368
00:15:23,616 --> 00:15:26,736
Even though the 600 dollars
is in there, this just looks

369
00:15:26,736 --> 00:15:29,236
like a mess, and this
is what would come back

370
00:15:29,236 --> 00:15:30,326
if I wrote a program

371
00:15:30,526 --> 00:15:33,406
that requested a URL
pretending it's a web page.

372
00:15:33,626 --> 00:15:36,546
Browsers of course know how to
render this nice and prettily

373
00:15:36,546 --> 00:15:37,886
like this in a web page.

374
00:15:38,026 --> 00:15:40,866
But if I'm writing a command
line program with PHP,

375
00:15:40,906 --> 00:15:43,456
now I have to pars or
analyze all of this code,

376
00:15:43,456 --> 00:15:44,836
and this is where
screen scraping,

377
00:15:45,116 --> 00:15:48,766
the process of writing a program
that just crosses its fingers

378
00:15:48,766 --> 00:15:51,696
that that web page structurally
is gonna stay the same day

379
00:15:51,696 --> 00:15:53,406
after day so you
can just grab data

380
00:15:53,406 --> 00:15:55,356
from it is actually nontrivial.

381
00:15:55,396 --> 00:15:57,636
We as a course actually
do this every night

382
00:15:57,846 --> 00:16:00,256
with Harbor Dining
Services website to grab all

383
00:16:00,256 --> 00:16:02,526
of the meal data
everyday so that you guys

384
00:16:02,526 --> 00:16:04,676
for your final projects can
use that kind of information.

385
00:16:04,676 --> 00:16:07,166
But long story short,
it's not fun, generally,

386
00:16:07,166 --> 00:16:08,686
though sometimes you
have to resort to it,

387
00:16:08,916 --> 00:16:11,366
but what caught our eye is
at the bottom of this page

388
00:16:11,996 --> 00:16:14,926
under this thing they called
toolbox is download data.

389
00:16:14,926 --> 00:16:16,936
And in fact when
I hover over this,

390
00:16:17,186 --> 00:16:18,546
I see that this is just a URL.

391
00:16:18,546 --> 00:16:20,836
It's gonna look a little
small here but I can see

392
00:16:20,836 --> 00:16:24,626
that this download data link is
just another URL, a get request

393
00:16:24,626 --> 00:16:28,156
where S equals GOOG and
then F equals a long string

394
00:16:28,156 --> 00:16:29,056
and then CSV.

395
00:16:29,056 --> 00:16:31,986
CSV is comma-separated
values and it's sort

396
00:16:31,986 --> 00:16:33,716
of a poor man's Excel file.

397
00:16:33,716 --> 00:16:37,146
It's a spreadsheet but it just
uses commas to separate columns.

398
00:16:37,386 --> 00:16:41,176
And so if you have a program
like Microsoft Excel that knows

399
00:16:41,176 --> 00:16:43,106
to look for commas as delimiters

400
00:16:43,106 --> 00:16:45,116
between what conceptually
should be commas,

401
00:16:45,346 --> 00:16:47,786
you can then open this file
in something like Excel.

402
00:16:47,786 --> 00:16:49,766
So I'm gonna go ahead
and click download data.

403
00:16:50,056 --> 00:16:52,856
It indeed says I'm downloading
a file called quotes.csv,

404
00:16:52,856 --> 00:16:55,186
so let me go ahead
and save that.

405
00:16:55,186 --> 00:16:58,256
And then if I double click
this file, because I have Excel

406
00:16:58,256 --> 00:17:00,646
on this particular computer,
it's Excel that opens.

407
00:17:00,646 --> 00:17:03,376
And what's really neat is
that I have the illusion

408
00:17:03,376 --> 00:17:06,076
of some columns here,
GOOG in the left column.

409
00:17:06,076 --> 00:17:08,856
Then what appears to be its
last trade price, what appears

410
00:17:08,856 --> 00:17:11,596
to be the date at which
it was last traded today,

411
00:17:11,596 --> 00:17:13,506
the time at which it
was last traded today.

412
00:17:13,806 --> 00:17:16,206
There are of course slight delay
is in a lot of these websites

413
00:17:16,206 --> 00:17:17,686
which is why it's
trailing by a few minutes,

414
00:17:17,896 --> 00:17:20,196
and then some other data that
if I compare back and forth

415
00:17:20,196 --> 00:17:22,086
with the website, I
could figure out which

416
00:17:22,086 --> 00:17:23,176
of these fields means what.

417
00:17:23,416 --> 00:17:25,246
But if I actually
look at the text file

418
00:17:25,246 --> 00:17:29,476
that I just downloaded, this is
just a file called quotes.csv.

419
00:17:29,476 --> 00:17:33,396
If I actually open this with
something like text edit,

420
00:17:33,396 --> 00:17:37,576
this simple little text program,
notice that's all in this--

421
00:17:37,666 --> 00:17:41,196
all that's in this file is that
data there separated by commas.

422
00:17:41,196 --> 00:17:44,486
And now, as a programmer, this
is really interesting to me

423
00:17:44,486 --> 00:17:47,416
because now I don't have
all this [inaudible] of HTML

424
00:17:47,416 --> 00:17:49,616
and hyperlinks and
colors and fonts,

425
00:17:49,616 --> 00:17:51,306
all these useless information.

426
00:17:51,576 --> 00:17:53,136
All I have now is the raw data.

427
00:17:53,136 --> 00:17:55,626
So this caught our eye, and
so what you'll do in problem,

428
00:17:55,626 --> 00:17:59,956
set 7 for instance, is write
code that calls a function

429
00:17:59,956 --> 00:18:01,956
that we wrote that
grabs this URL

430
00:18:02,366 --> 00:18:04,806
that has a stock symbol in it.

431
00:18:04,806 --> 00:18:06,986
Whatever stock symbol you
wanna pass in as an argument

432
00:18:06,986 --> 00:18:09,486
to this function, we make
the request to the web page,

433
00:18:09,726 --> 00:18:11,826
get back what essentially
is an Excel file.

434
00:18:11,946 --> 00:18:15,606
A CSV file, we then split
it on all these commas

435
00:18:15,826 --> 00:18:19,256
and then hand you back a struct
essentially called a class

436
00:18:19,286 --> 00:18:22,226
in PHP that contains all of
these interesting information.

437
00:18:22,486 --> 00:18:25,066
Now, not to dwell too much on
Yahoo Finance, but moving ahead,

438
00:18:25,066 --> 00:18:28,946
whether it's for your research
in the physical sciences

439
00:18:28,946 --> 00:18:31,786
or biological science or
economics or really any field

440
00:18:31,906 --> 00:18:34,056
where you might actually
wanna analyze data

441
00:18:34,056 --> 00:18:36,166
or manipulate something or do
something more efficiently,

442
00:18:36,166 --> 00:18:38,396
then you, the human could
do by a copy and paste,

443
00:18:38,736 --> 00:18:41,246
looking on the web or
looking on computers

444
00:18:41,246 --> 00:18:44,536
for actually machine
readable data like this is

445
00:18:44,536 --> 00:18:45,976
where things get
really interesting

446
00:18:45,976 --> 00:18:48,086
because it means you
can automate so much.

447
00:18:48,086 --> 00:18:50,476
And the simplest thing we
automated last week, recall,

448
00:18:50,656 --> 00:18:53,656
was simply automating the
idea of freshmen intramurals.

449
00:18:53,936 --> 00:18:56,196
And what we were able
to do last week is

450
00:18:56,246 --> 00:18:59,366
when the user submits a
form saying this is my name,

451
00:18:59,366 --> 00:19:02,016
this is my dorm, my gender,
I'm gonna be a captain or not,

452
00:19:02,376 --> 00:19:05,616
we were able to first completely
throw that information away,

453
00:19:05,816 --> 00:19:07,556
which clearly was
not all that useful.

454
00:19:07,556 --> 00:19:09,546
We just said, you're
registered but not really.

455
00:19:09,776 --> 00:19:13,176
But in the third version of
last week's Frosh IMs example,

456
00:19:13,176 --> 00:19:16,336
what did I finally
do with that data.

457
00:19:16,516 --> 00:19:19,336
Yeah, so I sent myself an
email, and back in the day,

458
00:19:19,336 --> 00:19:21,926
this would have been an email
not to me but to the proctor

459
00:19:21,926 --> 00:19:23,796
who was actually running
the freshmen intramurals

460
00:19:23,796 --> 00:19:24,586
sports program.

461
00:19:24,786 --> 00:19:28,606
And if I take a look at that
code, what you'll see here is

462
00:19:28,606 --> 00:19:31,626
that this was register3.php.

463
00:19:31,626 --> 00:19:34,896
Recall that at the very tail
end of that last lecture,

464
00:19:35,186 --> 00:19:37,686
sending an email on a
computer program reduced

465
00:19:37,686 --> 00:19:39,246
to just a few lines of code.

466
00:19:39,416 --> 00:19:42,516
I had a few variables and recall
that in PHP, a variable starts

467
00:19:42,516 --> 00:19:44,116
with a dollar sign
just by convention,

468
00:19:44,396 --> 00:19:46,536
so I declared a variable
called two and just put

469
00:19:46,536 --> 00:19:47,706
in my own email address.

470
00:19:47,706 --> 00:19:50,706
And notice the similarities with
C, double quotes around strings,

471
00:19:51,026 --> 00:19:54,616
although as an aside in PHP,
you can often use single quotes

472
00:19:54,696 --> 00:19:57,536
as well, semicolon at the
end, so that's the same.

473
00:19:57,876 --> 00:20:00,656
Subject equals registration,
body equals--

474
00:20:00,656 --> 00:20:02,906
and this one got a little
interesting 'cause I didn't

475
00:20:02,906 --> 00:20:03,976
wanna send like a short phrase.

476
00:20:04,056 --> 00:20:07,016
>> I want kind of a longer
sentence and so I wrote

477
00:20:07,016 --> 00:20:11,626
out body equals this person just
registered colon backslash n

478
00:20:11,626 --> 00:20:14,186
backslash n 'cause I wanna
move the cursor down a couple

479
00:20:14,186 --> 00:20:14,906
of lines in the email.

480
00:20:14,906 --> 00:20:17,046
And then notice this,
the period.

481
00:20:17,136 --> 00:20:20,686
So the period or the dot is the
concatenation operator in PHP.

482
00:20:20,916 --> 00:20:23,556
So whereas in C, it's
really actually a pain

483
00:20:23,736 --> 00:20:26,246
to take one string and
add more string to it

484
00:20:26,246 --> 00:20:27,546
and more string and more string.

485
00:20:27,736 --> 00:20:30,126
Because remember that a
string in C is an array.

486
00:20:30,126 --> 00:20:32,236
An array usually has a
fixed amount of memory

487
00:20:32,396 --> 00:20:34,966
so you can't just blindly
add more and more characters

488
00:20:35,006 --> 00:20:37,586
to the end of it,
but in PHP, you can.

489
00:20:37,646 --> 00:20:39,876
Underneath the hood,
the same kind

490
00:20:39,876 --> 00:20:41,056
of magic is still happening.

491
00:20:41,056 --> 00:20:42,936
The same kind of memory
is getting allocated

492
00:20:42,936 --> 00:20:44,816
and deallocated as
needed but all

493
00:20:44,816 --> 00:20:46,446
of that is taken
care of for you.

494
00:20:46,676 --> 00:20:50,506
And so notice what I concatenate
on to that phrase is this.

495
00:20:51,006 --> 00:20:54,276
Dollar sign underscore post
bracket quote unquote name.

496
00:20:54,576 --> 00:20:57,546
So what was this thing called
dollar sign underscore post,

497
00:20:58,066 --> 00:20:58,876
generally speaking?

498
00:20:59,426 --> 00:21:04,276
What was the point
of this thing?

499
00:21:04,496 --> 00:21:05,126
Awkward silence.

500
00:21:06,216 --> 00:21:06,986
Someone must know.

501
00:21:07,706 --> 00:21:09,816
Just conceptually like
what's-- what is this thing?

502
00:21:10,386 --> 00:21:10,946
>> It's an array.

503
00:21:11,046 --> 00:21:11,566
>> So it's an array.

504
00:21:11,916 --> 00:21:13,766
So it's an array and you
can infer that frankly

505
00:21:13,766 --> 00:21:15,026
from the square brackets.

506
00:21:15,026 --> 00:21:18,326
The notation is just like C.
We don't have a number inside

507
00:21:18,326 --> 00:21:20,996
of those square brackets but
this is because we get a new

508
00:21:20,996 --> 00:21:24,486
and improved version in array
called an associate of array

509
00:21:24,616 --> 00:21:27,556
in PHP, whereby the indices,
the things that you use to index

510
00:21:27,556 --> 00:21:30,026
into the array no longer
have to be numbers.

511
00:21:30,026 --> 00:21:32,816
They can actually be words
or phrases, sentences

512
00:21:32,946 --> 00:21:35,716
or more generally,
things called keys.

513
00:21:35,966 --> 00:21:41,076
And so what I can now do is grab
the value inside of this array

514
00:21:41,076 --> 00:21:43,376
at the location called name.

515
00:21:43,586 --> 00:21:43,726
Yeah.

516
00:21:44,516 --> 00:21:49,276
[ Inaudible Remark ]

517
00:21:49,776 --> 00:21:50,726
>> Good question.

518
00:21:50,726 --> 00:21:53,296
What if you use the
same syntax and I say,

519
00:21:53,296 --> 00:21:54,676
you know what I actually
want to include

520
00:21:54,676 --> 00:21:57,196
in this email even though I'm
completely making this up,

521
00:21:57,196 --> 00:22:01,166
I wanna say the value
of the foo key, F-O-O.

522
00:22:01,336 --> 00:22:03,716
Well, what would come back is
essentially the "empty string",

523
00:22:03,716 --> 00:22:05,406
nothing would actually happen.

524
00:22:06,896 --> 00:22:08,346
Alright, so maybe that's okay

525
00:22:08,346 --> 00:22:10,076
if it wasn't actually
a required field

526
00:22:10,196 --> 00:22:12,256
but in this case I know what
these fields were called.

527
00:22:12,416 --> 00:22:15,576
Now what's special about dollar
sign underscore post is that,

528
00:22:15,576 --> 00:22:16,356
yes, it's an array.

529
00:22:16,356 --> 00:22:17,826
Yes, it's an associate of array

530
00:22:18,046 --> 00:22:20,596
but it's generally what
PHP calls a super global.

531
00:22:20,596 --> 00:22:23,346
It's a special global variable
that you just get handed

532
00:22:23,346 --> 00:22:26,716
for free anytime you
write a PHP based website

533
00:22:27,086 --> 00:22:30,466
that is automatically
filled with any parameters

534
00:22:30,466 --> 00:22:33,996
that were submitted by some
user via form submissions.

535
00:22:34,076 --> 00:22:36,136
So remember we had the
whole premise here was

536
00:22:36,136 --> 00:22:38,906
that we made a form, open
bracket form in HTML.

537
00:22:39,186 --> 00:22:41,826
Recall that we specified
method equals something rather,

538
00:22:41,826 --> 00:22:43,586
so let me actually pull that up.

539
00:22:43,896 --> 00:22:46,636
Froshims3.php, recall that
we introduced this notion

540
00:22:46,636 --> 00:22:50,526
of a form last week, and this is
fairly self explanatory once you

541
00:22:50,526 --> 00:22:52,976
start-- once you get
the hang of the tags,

542
00:22:53,286 --> 00:22:59,036
up at the top here we have form
action equals register3.php.

543
00:22:59,036 --> 00:23:01,396
So action just says, what
is the action of this form?

544
00:23:01,396 --> 00:23:03,136
Where does it send its data to?

545
00:23:03,136 --> 00:23:04,716
Where does the data
get submitted?

546
00:23:04,906 --> 00:23:06,556
And I decided that in addition

547
00:23:06,556 --> 00:23:09,126
to this file called
froshims3.php,

548
00:23:09,126 --> 00:23:12,016
I'm gonna write a file
called register3.php.

549
00:23:12,016 --> 00:23:14,976
The purpose in life is to
receive the form submission

550
00:23:15,056 --> 00:23:16,466
from this particular page.

551
00:23:16,656 --> 00:23:18,696
Alright, the method
I'm gonna use is POST

552
00:23:18,866 --> 00:23:20,856
and we quickly mentioned
this last week,

553
00:23:21,076 --> 00:23:22,606
there's two main methods.

554
00:23:22,606 --> 00:23:24,096
One is POST and one is GET.

555
00:23:24,196 --> 00:23:25,886
And what's perhaps the
most obvious difference

556
00:23:25,886 --> 00:23:29,696
between the two?

557
00:23:29,696 --> 00:23:29,926
[ Inaudible Remark ]

558
00:23:29,926 --> 00:23:32,786
>> Yeah, so using
method equals "GET" means

559
00:23:32,786 --> 00:23:34,796
that the parameter
show up in the URL.

560
00:23:35,056 --> 00:23:38,106
So in the case of Yahoo Finance,
when I filled out that form

561
00:23:38,106 --> 00:23:40,986
in the top left corner and
type GOOG and hit enter,

562
00:23:41,196 --> 00:23:43,316
notice that-- recall
that the URL changed

563
00:23:43,506 --> 00:23:46,146
and you could actually see
what I typed in the URL,

564
00:23:46,146 --> 00:23:47,876
and so that's because
underneath the hood,

565
00:23:47,876 --> 00:23:49,816
Yahoo must be using
the GET method.

566
00:23:50,126 --> 00:23:52,206
Now why is that a
good thing perhaps?

567
00:23:53,796 --> 00:23:54,406
Why use GET?

568
00:23:54,406 --> 00:23:54,576
Yeah.

569
00:23:55,646 --> 00:23:57,136
>> Bookmark it.

570
00:23:57,136 --> 00:23:58,356
>> Yeah, so you can
bookmark it, right?

571
00:23:58,356 --> 00:24:01,396
If you wanna add a bookmark to
your browser, if you wanna copy

572
00:24:01,396 --> 00:24:02,556
and paste it into an email,

573
00:24:02,906 --> 00:24:05,146
what's nice about the
GET method is that state,

574
00:24:05,236 --> 00:24:06,336
the state of the world

575
00:24:06,336 --> 00:24:09,266
as you currently see it is
embedded inside of the URL

576
00:24:09,266 --> 00:24:10,616
so the state is retained.

577
00:24:10,616 --> 00:24:11,866
Someone else can
follow that link

578
00:24:12,016 --> 00:24:13,846
and see exactly the
same thing as you.

579
00:24:14,036 --> 00:24:16,226
Now this is probably not the
best method if you're trying

580
00:24:16,226 --> 00:24:17,486
to log into some account.

581
00:24:17,836 --> 00:24:20,096
You fill out a form with
your user name and password

582
00:24:20,096 --> 00:24:22,436
or maybe your credit
card number and your 3

583
00:24:22,436 --> 00:24:25,546
or 4 digit secret code on the
back of it and then hit submit.

584
00:24:25,846 --> 00:24:28,966
Well, it's probably not a huge
deal if you're sitting at home

585
00:24:29,186 --> 00:24:31,456
or in your dorm and the
form is getting submitted

586
00:24:31,456 --> 00:24:33,366
from your own laptop
to some server.

587
00:24:33,516 --> 00:24:34,966
But if you're on
a public machine

588
00:24:34,966 --> 00:24:38,026
or if other roommates are in the
habit of using your computer,

589
00:24:38,256 --> 00:24:41,066
anytime the URL changes
that's in your browser,

590
00:24:41,186 --> 00:24:43,286
what's a side effect
of using GET?

591
00:24:43,416 --> 00:24:44,996
What's that?

592
00:24:45,136 --> 00:24:49,916
>> Password shows
up as a plain text.

593
00:24:49,916 --> 00:24:51,886
>> Yeah, so the password is
gonna show up as plain text

594
00:24:51,966 --> 00:24:53,926
in the URL, or more
specifically,

595
00:24:54,136 --> 00:24:56,226
your history is going
to remember

596
00:24:56,226 --> 00:24:57,486
that you visited that URL.

597
00:24:57,946 --> 00:25:00,566
So if you've ever gotten a
little nosy and crossed that,

598
00:25:00,566 --> 00:25:01,826
let's call it unethical line,

599
00:25:02,026 --> 00:25:04,146
and poked around at
what URL is your friends

600
00:25:04,146 --> 00:25:05,856
or roommates have
actually been visiting,

601
00:25:05,856 --> 00:25:07,396
it's got to be a few
of you here, right?

602
00:25:07,396 --> 00:25:09,406
So that's the so called
history of a browser,

603
00:25:09,526 --> 00:25:12,586
and that pretty much records
pretty much every GET request

604
00:25:12,586 --> 00:25:13,866
that was made with the browser,

605
00:25:14,116 --> 00:25:15,826
it's just logged
in that drop-down.

606
00:25:15,856 --> 00:25:18,706
And of course you can go to
like tools and options and clear

607
00:25:18,706 --> 00:25:22,476
that kind of cache, but GET is
not very good for privacy sake.

608
00:25:22,506 --> 00:25:25,506
POST is generally better for
that and POST is actually called

609
00:25:25,506 --> 00:25:28,346
for anytime you wanna have
the user upload something

610
00:25:28,346 --> 00:25:29,686
like a JPEG to Facebook,

611
00:25:29,926 --> 00:25:33,526
you can't really fit an image
conceptually or even technically

612
00:25:33,716 --> 00:25:37,156
in a URL, you can change it
to zeros and ones or some kind

613
00:25:37,256 --> 00:25:40,326
of encoding but it doesn't
really fit very well in the URL.

614
00:25:40,326 --> 00:25:42,826
So, POST is also used when
you wanna submit large amounts

615
00:25:42,826 --> 00:25:43,556
of information.

616
00:25:43,866 --> 00:25:46,106
But the relevance to
the Frosh IMs example is

617
00:25:46,106 --> 00:25:48,726
that inside this form,
there's an input called name.

618
00:25:48,996 --> 00:25:50,446
There's an input called captain.

619
00:25:50,506 --> 00:25:53,346
There's an input called gender
and each of this happens to be

620
00:25:53,346 --> 00:25:54,656
of slightly different types.

621
00:25:54,736 --> 00:25:56,576
I know this by just
having read the manual

622
00:25:56,576 --> 00:25:59,846
or having learned how HTML works
and so I know that in input,

623
00:26:00,056 --> 00:26:02,976
its type can be text if
you want a text field.

624
00:26:02,976 --> 00:26:04,796
It can be check box if
you want a check box.

625
00:26:05,116 --> 00:26:06,646
Radio, if you want
a radio button,

626
00:26:06,826 --> 00:26:07,876
and there're a few others.

627
00:26:07,876 --> 00:26:09,746
But pretty much it's
straightforward

628
00:26:09,746 --> 00:26:12,286
as just saying what piece of--
or what type of data you want.

629
00:26:12,826 --> 00:26:17,226
But because the action of
this form was register3.php,

630
00:26:17,226 --> 00:26:20,896
what happens when I actually
click submit is that this page,

631
00:26:20,946 --> 00:26:23,866
register3.php, which
lives at a URL.

632
00:26:24,186 --> 00:26:28,046
If I go to this in a browser,
I can absolutely visit this.

633
00:26:28,046 --> 00:26:31,616
I can go to froshim3.php which,
recall, looked like this.

634
00:26:31,986 --> 00:26:36,876
I can also go directly to
register3.php but notice that--

635
00:26:37,596 --> 00:26:39,486
let me disable this
for a moment.

636
00:26:40,316 --> 00:26:41,996
I'm gonna do one
quick thing here.

637
00:26:41,996 --> 00:26:45,176
Print, yes, here exit.

638
00:26:45,436 --> 00:26:48,576
Just to prove that this file
called register3.php can

639
00:26:48,736 --> 00:26:51,476
in fact be visited
directly, I click here,

640
00:26:51,766 --> 00:26:54,426
and indeed this is now just
a web page on the internet.

641
00:26:54,426 --> 00:26:57,566
It's not actually returning
legit HTML yet, but the URL is

642
00:26:57,566 --> 00:26:59,336
in fact web accessible.

643
00:26:59,556 --> 00:27:02,006
So, I'm not actually
submitting any parameters

644
00:27:02,006 --> 00:27:03,886
to this form right now
but if I get rid of this,

645
00:27:04,316 --> 00:27:08,316
and actually access register
3 by going to froshims3

646
00:27:08,316 --> 00:27:12,716
and saying, I am David, I'll be
a captain and Mathews register,

647
00:27:13,156 --> 00:27:15,186
now it claims you are
registered really.

648
00:27:15,376 --> 00:27:17,806
Notice I'm again
at register3.php,

649
00:27:17,916 --> 00:27:20,206
so that begs the question,
what happened this time?

650
00:27:20,386 --> 00:27:22,936
Well, if we look at this
code, notice at the very top

651
00:27:22,936 --> 00:27:27,436
of the file, register3.php,
notice the very first character,

652
00:27:27,436 --> 00:27:28,876
open bracket question mark.

653
00:27:28,876 --> 00:27:30,656
This says here comes
some PHP code.

654
00:27:30,946 --> 00:27:33,086
Then the rest of the stuff for
a little while is just comments,

655
00:27:33,086 --> 00:27:34,766
so uninteresting for
our purposes now.

656
00:27:35,006 --> 00:27:37,586
But down here, we
actually see some logic

657
00:27:37,966 --> 00:27:39,756
and then we see close bracket--

658
00:27:39,756 --> 00:27:41,996
close question mark
close bracket

659
00:27:42,216 --> 00:27:43,806
which means end of PHP mode.

660
00:27:43,806 --> 00:27:45,446
So what is this PHP code doing?

661
00:27:45,796 --> 00:27:49,096
Well, it is this code
that sort of magically,

662
00:27:49,166 --> 00:27:51,306
thanks to its being
accessed by the web,

663
00:27:51,306 --> 00:27:54,976
has access to a superglobal
associative array,

664
00:27:55,316 --> 00:27:58,216
inside of which are all those
key value pairs from the form

665
00:27:58,216 --> 00:27:59,386
that I myself created.

666
00:27:59,576 --> 00:28:01,936
So if I had made a much
longer form with ten fields,

667
00:28:02,176 --> 00:28:05,976
this associative array would
have ten different keys inside

668
00:28:05,976 --> 00:28:07,716
of it handed to me
with the users input.

669
00:28:08,046 --> 00:28:09,356
So I first do a sanity check.

670
00:28:09,466 --> 00:28:14,956
If the name key in this ray, it
is not equal to quote unquote,

671
00:28:15,366 --> 00:28:19,086
and the gender keys value is
not equal to quote unquote

672
00:28:19,086 --> 00:28:23,016
and the dorm keys value is
not equal to quote unquote,

673
00:28:23,096 --> 00:28:26,906
what's the implication sort
of just in layman's terms?

674
00:28:26,906 --> 00:28:27,856
[ Inaudible Remark ]

675
00:28:27,856 --> 00:28:29,406
>> They build out
the form, right?

676
00:28:29,406 --> 00:28:33,386
They must-- because those
values are not the empty string

677
00:28:33,386 --> 00:28:34,616
because they're not blanks,

678
00:28:34,676 --> 00:28:36,566
obviously the user
typed something in

679
00:28:36,736 --> 00:28:37,676
and so they're not blank,

680
00:28:37,676 --> 00:28:39,346
and so now I wanna do
something with that.

681
00:28:39,346 --> 00:28:41,896
I'm going to assume without
doing much error checking

682
00:28:41,896 --> 00:28:43,136
in this version,
but you know what,

683
00:28:43,136 --> 00:28:44,416
this person just registered.

684
00:28:44,416 --> 00:28:46,986
So I'm gonna compose
this email to the proctor

685
00:28:46,986 --> 00:28:48,196
or to myself in this case.

686
00:28:48,476 --> 00:28:50,896
I'm gonna-- I read the
manual to figure out that

687
00:28:50,896 --> 00:28:53,516
if I wanna send it from
myself, I can just say from:

688
00:28:53,516 --> 00:28:57,366
malan@cs50.net and then the
stupid convention here backslash

689
00:28:57,366 --> 00:28:59,896
r backslash n, you might
recall that, but that was just

690
00:28:59,896 --> 00:29:00,866
from the documentation.

691
00:29:01,156 --> 00:29:03,486
But the real magic is
just in this one line.

692
00:29:03,566 --> 00:29:06,176
It turns out that there is
a function built into PHP,

693
00:29:06,176 --> 00:29:09,176
definitely doesn't exist
in C, that is called mail,

694
00:29:09,416 --> 00:29:12,826
it takes 4 arguments, in
this case, the two argument,

695
00:29:12,856 --> 00:29:15,416
the subject, the body and then
those things called headers,

696
00:29:15,416 --> 00:29:16,966
the additional metadata
at the top.

697
00:29:17,166 --> 00:29:19,356
And the end result,
recall, was that I was able

698
00:29:19,356 --> 00:29:21,126
to send an email to myself.

699
00:29:21,366 --> 00:29:23,816
And if I actually go
check my mail now here

700
00:29:24,646 --> 00:29:27,686
in this Gmail interface, this
is what the proctor would see.

701
00:29:27,966 --> 00:29:32,016
But here is the sort of tidbit
that's worth mentioning perhaps

702
00:29:32,016 --> 00:29:33,466
for security and privacy sake.

703
00:29:33,726 --> 00:29:35,986
If I actually view the
details of this, indeed,

704
00:29:36,226 --> 00:29:39,686
it looks like I've sent an
email from myself to myself.

705
00:29:40,156 --> 00:29:44,136
But it looks like with this
programming power, I can say,

706
00:29:44,136 --> 00:29:46,736
you know what, I don't want
these emails coming from me.

707
00:29:46,736 --> 00:29:51,896
I want them coming from
Cansu, aydede@fas.harvard.edu.

708
00:29:52,546 --> 00:29:55,116
Save that, Cansu
is not here today.

709
00:29:55,636 --> 00:29:57,716
So, now I'm gonna
go back to my inbox.

710
00:29:57,926 --> 00:29:59,036
I'm gonna go back to the form.

711
00:29:59,036 --> 00:30:02,296
I'm gonna reregister as,
let's say, Yuhki this time,

712
00:30:02,706 --> 00:30:03,976
also for Mathews, register.

713
00:30:04,936 --> 00:30:05,756
>> Says I'm registered.

714
00:30:05,756 --> 00:30:08,266
Let's go to CS50
mail, reload the page.

715
00:30:08,426 --> 00:30:09,656
Oh, Cansu emailed me.

716
00:30:10,036 --> 00:30:13,936
And indeed I have an email now
from aydede@fas.harvard.edu.

717
00:30:14,256 --> 00:30:15,896
So, don't even get us started

718
00:30:15,896 --> 00:30:17,686
on the insecurity
of email, frankly.

719
00:30:17,686 --> 00:30:20,836
There is absolutely no
fundamental authentication built

720
00:30:20,836 --> 00:30:22,966
into the email accounts
that you and I use everyday.

721
00:30:23,316 --> 00:30:25,386
Very often, if you have
a sponsored account

722
00:30:25,386 --> 00:30:26,856
with a university or a company,

723
00:30:27,166 --> 00:30:29,986
the system administrators
could very well prevent you

724
00:30:29,986 --> 00:30:32,716
from changing that
address to something else.

725
00:30:33,066 --> 00:30:34,906
But even I use Gmail
all the time.

726
00:30:34,906 --> 00:30:36,806
Yet if you've ever gotten
an email from me personally,

727
00:30:36,806 --> 00:30:38,476
it still says harvard.edu

728
00:30:38,476 --> 00:30:40,516
because I'm essentially
spoofing the from address.

729
00:30:40,876 --> 00:30:43,636
Now sometimes when you do
this, you increase the risk

730
00:30:43,636 --> 00:30:45,166
of your email getting
flagged as spam

731
00:30:45,336 --> 00:30:48,246
because servers are getting
increasingly sophisticated

732
00:30:48,516 --> 00:30:51,536
and they realize, wait a
minute, this is from harvard.edu

733
00:30:51,536 --> 00:30:53,496
but it clearly came
from Google servers

734
00:30:53,496 --> 00:30:55,196
on the West Coast,
this can't be.

735
00:30:55,196 --> 00:30:56,826
This feels like it's
probably spam.

736
00:30:57,196 --> 00:30:59,496
So it's not a perfect
system, but fundamentally now,

737
00:30:59,496 --> 00:31:01,636
emails are very easily forged.

738
00:31:01,636 --> 00:31:04,406
And that's why I was able to
get that email about the 123--

739
00:31:04,466 --> 00:31:09,126
what was that,
123contactform.com.

740
00:31:09,466 --> 00:31:11,026
It's just as easy for spammers

741
00:31:11,026 --> 00:31:12,656
to forge any one
of our addresses.

742
00:31:12,656 --> 00:31:14,746
So as a rule of thumb, if
you ever do get an email

743
00:31:14,746 --> 00:31:17,736
that perhaps seems to be
forged, frankly what you can do

744
00:31:17,736 --> 00:31:19,896
in various email
clients including Google,

745
00:31:20,116 --> 00:31:21,296
if you look at the original,

746
00:31:21,336 --> 00:31:23,626
you'll see some interesting
things, and we won't spend time

747
00:31:23,626 --> 00:31:26,986
on this here but every
line in the original part

748
00:31:26,986 --> 00:31:29,806
of an email shows you the
IP address or the name

749
00:31:29,806 --> 00:31:31,656
of the server that this
email passed through.

750
00:31:31,796 --> 00:31:34,246
So you can often do a bit
of forensics and infer

751
00:31:34,246 --> 00:31:36,966
from these headers where this
email actually came from.

752
00:31:36,966 --> 00:31:38,876
And if we dwelled on this
example, we would see that,

753
00:31:38,876 --> 00:31:42,086
it came from aydede@fas
and yet entirely

754
00:31:42,086 --> 00:31:44,796
through Google server,
so how could that be.

755
00:31:44,906 --> 00:31:47,316
Or actually not even
Harvard's Google servers,

756
00:31:47,806 --> 00:31:51,006
in this case it came from
our own cloud server,

757
00:31:51,006 --> 00:31:54,386
which is not FAS, it's of
course CS50's own domain.

758
00:31:54,386 --> 00:31:57,896
So I would be remiss if I didn't
say don't actually do this.

759
00:31:57,896 --> 00:32:00,776
Actually I-- and I'll say
this from personal example.

760
00:32:00,776 --> 00:32:02,646
Freshman year, I was
really proud of my self

761
00:32:02,646 --> 00:32:03,466
when I learned this trick

762
00:32:03,466 --> 00:32:05,566
in how you can just put
any email address you want

763
00:32:05,566 --> 00:32:07,396
in your email client and
voila, send an email.

764
00:32:07,726 --> 00:32:13,326
So I made the unfortunate social
and perhaps political decision

765
00:32:13,596 --> 00:32:16,236
to send an email from someone
else in my proctor group,

766
00:32:16,516 --> 00:32:19,716
but like a complete moron
forgot that I sent out emails

767
00:32:19,716 --> 00:32:21,546
at the time with an
automatic signature

768
00:32:21,546 --> 00:32:22,746
which happened to say DJM.

769
00:32:23,346 --> 00:32:25,196
So this email I sent to
my whole proctor group

770
00:32:25,196 --> 00:32:29,136
on some stupid kind of issue
has made some point on behalf

771
00:32:29,136 --> 00:32:31,366
of a roommate whose opinion
I was trying to change,

772
00:32:31,366 --> 00:32:33,516
whatever the stupid-- the
story was at the time.

773
00:32:33,876 --> 00:32:38,326
And it was like sincerely Joe
or whoever the person was, DJM.

774
00:32:38,326 --> 00:32:38,576
[ Laughter ]

775
00:32:38,576 --> 00:32:38,796
>> Caught.

776
00:32:39,316 --> 00:32:42,216
That was not a good time.

777
00:32:42,216 --> 00:32:45,716
So, again, do as I say,
not as I actually do.

778
00:32:45,716 --> 00:32:47,756
Kind of recurring
theme here perhaps.

779
00:32:48,216 --> 00:32:51,306
So-- but really the
takeaway for today is

780
00:32:51,306 --> 00:32:54,126
that the cool power
here is our ability now

781
00:32:54,126 --> 00:32:57,766
to automate very mundane,
very tedious tasks and also

782
00:32:57,766 --> 00:32:59,126
to have these processes scale.

783
00:32:59,126 --> 00:33:01,096
Frankly, one of the neatest
things about being able

784
00:33:01,096 --> 00:33:02,586
to make a website
that's not static,

785
00:33:02,806 --> 00:33:04,746
but that's dynamic using
a language like PHP

786
00:33:04,746 --> 00:33:07,896
and we'll see today using
a database like MySQL is

787
00:33:07,896 --> 00:33:09,236
that you write this kind of code

788
00:33:09,236 --> 00:33:11,106
and then you walk
away, you go to dinner.

789
00:33:11,106 --> 00:33:13,706
You go about your business
and the thing runs itself.

790
00:33:13,746 --> 00:33:15,786
Frosh IMs continues
to get registrations.

791
00:33:16,056 --> 00:33:18,496
Some of you have probably RSVP'd
for the movie already and that's

792
00:33:18,496 --> 00:33:20,936
because we set up a form that's
doing that automatically.

793
00:33:21,126 --> 00:33:24,736
So you really get this ability
to automate processes and free

794
00:33:24,736 --> 00:33:25,816
up your own human cycles

795
00:33:25,816 --> 00:33:28,016
to solve much more
interesting problems.

796
00:33:28,016 --> 00:33:29,006
We do this all of the time.

797
00:33:29,006 --> 00:33:31,586
Certainly this semester,
with 500 some students,

798
00:33:31,826 --> 00:33:33,546
anytime you submit
those damn forms,

799
00:33:33,546 --> 00:33:36,146
we get 500 new submissions
to deal with

800
00:33:36,326 --> 00:33:38,576
but we automate the
process of dispatching all

801
00:33:38,576 --> 00:33:40,626
of your individual responses
to your teaching fellow.

802
00:33:40,626 --> 00:33:43,736
We synchronize with the server
to do so and really humans have

803
00:33:43,736 --> 00:33:46,166
to be relatively
uninvolved in that process.

804
00:33:46,166 --> 00:33:48,136
So, you can start to
do some neat things

805
00:33:48,136 --> 00:33:49,986
that benefit you, the person.

806
00:33:50,046 --> 00:33:51,886
Alright. So, what
more can we do?

807
00:33:51,886 --> 00:33:54,766
Well, let's take a
look at froshims4.php

808
00:33:54,766 --> 00:33:57,756
and inch our way toward actually
using a database 'cause frankly

809
00:33:57,756 --> 00:34:01,126
at some point, the proctor's
expectations are going to rise.

810
00:34:01,126 --> 00:34:02,736
And he or she is
not gonna be cool

811
00:34:02,736 --> 00:34:04,456
with getting an email
every time one

812
00:34:04,456 --> 00:34:06,706
of 1600 freshmen
registers for a sport.

813
00:34:06,986 --> 00:34:08,586
It'd much rather
this information end

814
00:34:08,586 --> 00:34:11,526
up in a spreadsheet or end
up in a database so that he

815
00:34:11,526 --> 00:34:14,296
or she can look at it
anytime they want but not have

816
00:34:14,346 --> 00:34:16,526
to manually copy and
paste from this email.

817
00:34:16,526 --> 00:34:20,116
So in 1996 or whatever, sending
an email, this was improvement,

818
00:34:20,116 --> 00:34:21,186
'cause it meant no more paper.

819
00:34:21,416 --> 00:34:22,466
But we can do much better

820
00:34:22,466 --> 00:34:24,576
and we can do much
better relatively easily.

821
00:34:24,856 --> 00:34:26,206
So first, take notice of this.

822
00:34:26,906 --> 00:34:31,536
This is froshims4.php and you
may encounter this paradigm

823
00:34:31,536 --> 00:34:35,156
in section or an example code
that you see in books or online,

824
00:34:35,156 --> 00:34:38,146
realize the action of
a form does not need

825
00:34:38,146 --> 00:34:39,566
to point to a separate file.

826
00:34:39,616 --> 00:34:42,366
You'll see in problem set 7
that we do this consistently.

827
00:34:42,366 --> 00:34:44,776
We have one file,
say, login.php submit

828
00:34:45,016 --> 00:34:47,866
to login2.php 'cause
I think in terms

829
00:34:47,866 --> 00:34:49,556
of the mental model,
it's nice and simple.

830
00:34:49,556 --> 00:34:51,536
There's step 1 and
then there's step 2.

831
00:34:51,606 --> 00:34:53,866
But realize once you
now have the ability

832
00:34:53,866 --> 00:34:56,776
to write this code yourself,
you can actually have,

833
00:34:56,776 --> 00:35:01,956
as in this case, a file called
froshims4.php submit back

834
00:35:02,096 --> 00:35:02,866
to its self.

835
00:35:03,596 --> 00:35:06,746
Now why in the world would you
want a web page like a form

836
00:35:06,946 --> 00:35:10,326
to submit not to a different
URL but to the same exact URL,

837
00:35:10,626 --> 00:35:11,826
to the same file, in fact?

838
00:35:12,866 --> 00:35:17,926
What might be the value in that?

839
00:35:19,416 --> 00:35:19,536
Some [inaudible].

840
00:35:19,536 --> 00:35:19,603
Yeah.

841
00:35:19,603 --> 00:35:19,746
[ Inaudible Remark ]

842
00:35:19,746 --> 00:35:22,276
>> Update the what?

843
00:35:22,466 --> 00:35:24,346
So, update the web
page of the user data.

844
00:35:24,526 --> 00:35:26,606
Possibly, possibly.

845
00:35:26,606 --> 00:35:29,546
Let me point out one of
the sort of downsides

846
00:35:29,546 --> 00:35:30,536
of this current approach.

847
00:35:30,536 --> 00:35:33,146
If I go back to register 3,

848
00:35:33,386 --> 00:35:35,996
suppose that I actually
don't fill out this form

849
00:35:35,996 --> 00:35:38,376
and just click register--
oh, actually what--

850
00:35:38,376 --> 00:35:39,556
I can't demo with this example.

851
00:35:39,766 --> 00:35:41,736
What happens on the
most annoying of sites?

852
00:35:41,736 --> 00:35:44,456
You click submit, you then get
to a page and it says, sorry,

853
00:35:44,486 --> 00:35:45,816
you need to provide
your email address.

854
00:35:45,816 --> 00:35:48,016
And then you have to hit the
back button and sometimes

855
00:35:48,016 --> 00:35:49,316
on this horribly
designed website,

856
00:35:49,316 --> 00:35:51,696
the whole form is then
blank and you have

857
00:35:51,696 --> 00:35:52,846
to start all over again.

858
00:35:53,066 --> 00:35:55,376
So if you're actually
sending the user from point A

859
00:35:55,376 --> 00:35:57,476
to point B, the problem is

860
00:35:57,476 --> 00:35:59,696
that point B is probably
gonna look different and

861
00:35:59,696 --> 00:36:02,106
yet if they made a mistake,
you want them to go fill

862
00:36:02,106 --> 00:36:05,226
out point A again, and so
why not just leave them there

863
00:36:05,276 --> 00:36:05,876
if possible.

864
00:36:05,876 --> 00:36:09,146
So, one of the tricks we can
see here in this next example is

865
00:36:09,146 --> 00:36:13,396
if I look at froshims5.php,
if I want to detect

866
00:36:14,106 --> 00:36:17,066
that an error has happened,
I can do this at the top

867
00:36:17,066 --> 00:36:19,536
of the same file and then
leverage this information.

868
00:36:19,656 --> 00:36:21,306
So, let's see what
this thing does.

869
00:36:21,306 --> 00:36:26,716
First, I'm gonna go to
froshims4, 5 rather .php.

870
00:36:26,716 --> 00:36:30,256
Let me suppress this error
message with a little trick

871
00:36:30,256 --> 00:36:32,276
for now, ignore that little
detail, I'll fix it later.

872
00:36:32,766 --> 00:36:36,966
Oh, another trick, ignore what I
just did there, fix that later.

873
00:36:37,196 --> 00:36:38,536
Okay. Dammit.

874
00:36:39,446 --> 00:36:43,856
Alright, close your eyes
for another moment, line 37,

875
00:36:44,176 --> 00:36:45,766
the server I'm using
is slightly different

876
00:36:45,766 --> 00:36:47,046
from the server you'll be using.

877
00:36:47,516 --> 00:36:48,136
That's my excuse.

878
00:36:49,716 --> 00:36:51,116
Alright, I'm losing
credibility today.

879
00:36:51,226 --> 00:36:52,476
Okay, perfect form, right?

880
00:36:52,526 --> 00:36:54,466
So now this is froshims5.

881
00:36:54,616 --> 00:36:56,376
Now suppose I just say,
alright, you don't need

882
00:36:56,376 --> 00:36:58,426
to know this information,
I'm just David, register.

883
00:36:58,956 --> 00:37:01,746
Dammit, line 15th.

884
00:37:02,146 --> 00:37:02,286
Here.

885
00:37:02,286 --> 00:37:03,776
[ Inaudible Remark ]

886
00:37:03,776 --> 00:37:04,486
>> This is fast.

887
00:37:04,616 --> 00:37:06,576
This is one line of
configuration on the server

888
00:37:06,576 --> 00:37:07,596
that will make that
problem go away.

889
00:37:08,076 --> 00:37:09,896
Okay, so notice here,
I said David.

890
00:37:09,996 --> 00:37:12,766
I clicked register and then
I got yelled at in red text

891
00:37:12,866 --> 00:37:14,096
but I'm on the same form.

892
00:37:14,316 --> 00:37:17,506
So it looks as though that
that red text you must fill

893
00:37:17,506 --> 00:37:19,926
out the form is maybe
being conditionally shown.

894
00:37:19,926 --> 00:37:23,576
And sure enough, if we just have
some logic in the same PHP file,

895
00:37:23,576 --> 00:37:25,476
we can check was there an error.

896
00:37:25,476 --> 00:37:27,496
If so, let me yell at the user,

897
00:37:27,496 --> 00:37:30,106
otherwise let me just
show the form as usual.

898
00:37:30,106 --> 00:37:35,156
So this is froshims5 and notice
that froshims5.php first of all,

899
00:37:35,286 --> 00:37:36,546
this is almost copy and paste

900
00:37:36,546 --> 00:37:37,836
from everything we've
seen thus far.

901
00:37:37,956 --> 00:37:39,246
So I gloss over some details.

902
00:37:39,546 --> 00:37:43,156
Notice that froshims5.php
submits back to itself.

903
00:37:43,226 --> 00:37:45,696
And that's what initially is
gonna enable this neat trick

904
00:37:45,916 --> 00:37:48,676
of having this immediate
feedback loop on the same page.

905
00:37:48,936 --> 00:37:50,866
But at the top of this
file, notice what I did,

906
00:37:51,376 --> 00:37:54,236
ignore all of these at signs.

907
00:37:54,236 --> 00:37:55,906
Though for those
perhaps more familiar,

908
00:37:55,906 --> 00:37:58,336
the at sign is essentially
suppressing these things called

909
00:37:58,336 --> 00:38:00,206
notices that we were
seeing, but again,

910
00:38:00,206 --> 00:38:02,216
we'll disable those
permanently for you.

911
00:38:03,096 --> 00:38:04,456
So notice this.

912
00:38:04,456 --> 00:38:09,816
If the value of the
action parameter is true,

913
00:38:09,916 --> 00:38:11,626
go ahead and do this.

914
00:38:11,626 --> 00:38:12,756
Well, what's going on here?

915
00:38:12,956 --> 00:38:15,566
Well notice here, I'm gonna wave
my hands at some of the details

916
00:38:15,566 --> 00:38:18,106
for now but notice
that if the value

917
00:38:18,106 --> 00:38:21,296
of name equals equals
blank or the value

918
00:38:21,296 --> 00:38:24,196
of gender equals equals
blank or the value

919
00:38:24,196 --> 00:38:26,816
of dorm equals equals
blank, this time,

920
00:38:26,956 --> 00:38:29,376
I'm actually gonna set a
variable called dollar sign

921
00:38:29,416 --> 00:38:32,486
error and just set
it equal to true.

922
00:38:32,766 --> 00:38:36,366
One of the minor
weaknesses in PHP is

923
00:38:36,366 --> 00:38:39,366
that it's case insensitive
sometimes but not always

924
00:38:39,456 --> 00:38:41,146
so you will see some
textbooks and resource

925
00:38:41,146 --> 00:38:42,346
that say uppercase true.

926
00:38:42,616 --> 00:38:44,126
Sometimes you'll
see lowercase true.

927
00:38:44,126 --> 00:38:45,956
Sometimes you'll
see capital T true.

928
00:38:46,236 --> 00:38:46,966
It's kind of a mess.

929
00:38:47,096 --> 00:38:50,096
I would just as always with
style be consistent so I'll go

930
00:38:50,096 --> 00:38:51,286
with uppercase this time around.

931
00:38:51,586 --> 00:38:53,356
And so now error is true.

932
00:38:53,506 --> 00:38:55,066
So notice what's
gonna happen here.

933
00:38:55,066 --> 00:38:57,456
If I scroll down,
notice this line of code.

934
00:38:57,926 --> 00:39:00,716
Recall that you can have
if conditions in PHP code

935
00:39:00,856 --> 00:39:03,936
and recall that you can
commingle PHP code and HTML.

936
00:39:04,186 --> 00:39:07,416
So notice I have HTML,
HTML, HTML, HTML.

937
00:39:07,416 --> 00:39:10,406
Oh, open bracket question
mark, here comes some PHP code,

938
00:39:10,406 --> 00:39:11,776
I'm gonna ask a question.

939
00:39:12,076 --> 00:39:15,676
If error is true, so again,
ignore the at sign for now.

940
00:39:15,676 --> 00:39:19,636
But if dollar sign error is
true, colon, do the following.

941
00:39:19,636 --> 00:39:23,196
So it's okay in PHP to then
exit PHP mode because so long

942
00:39:23,196 --> 00:39:25,386
as you've just answered
true to that question,

943
00:39:25,686 --> 00:39:27,816
only the following lines
are going to print.

944
00:39:28,196 --> 00:39:31,006
So, div style, so this
is where I get that red

945
00:39:31,006 --> 00:39:32,746
from div again is the
division of the page.

946
00:39:32,746 --> 00:39:34,076
Style is for CSS.

947
00:39:34,376 --> 00:39:36,136
Color colon red makes
the text red.

948
00:39:36,136 --> 00:39:37,766
And notice there,
there is that sentence.

949
00:39:37,766 --> 00:39:39,826
You must fill out the
form, exclamation point,

950
00:39:40,006 --> 00:39:42,666
and at the end of that is
going to be my close div tag

951
00:39:43,006 --> 00:39:45,516
which looks like
that, and then endif.

952
00:39:45,956 --> 00:39:47,446
So in short, I just
have a condition.

953
00:39:47,526 --> 00:39:50,126
In my PHP code, it
checks the value of error

954
00:39:50,126 --> 00:39:53,376
which I myself set at the top
of this file for the purposes

955
00:39:53,376 --> 00:39:54,936
of reminding my self later

956
00:39:54,936 --> 00:39:56,986
when I actually render
the web page was

957
00:39:56,986 --> 00:39:59,556
in fact there an
error in this case.

958
00:40:00,086 --> 00:40:02,436
>> But we're still not doing
anything with this information.

959
00:40:02,516 --> 00:40:05,566
So let's actually take
one more step toward that

960
00:40:05,716 --> 00:40:08,886
and also move away from hard
coding everything into our page.

961
00:40:08,886 --> 00:40:12,806
As soon as you find yourself in
pset7 or 8 or any final project,

962
00:40:13,076 --> 00:40:15,316
copying and pasting
on, it's probably time

963
00:40:15,316 --> 00:40:17,266
to start automating
the process somehow.

964
00:40:17,506 --> 00:40:20,206
So it turns out in PHP,
you can declare an array,

965
00:40:20,486 --> 00:40:23,606
just as you can in C, and you
can statically initialize it

966
00:40:23,606 --> 00:40:26,266
which means you can put values
in it right from the get-go.

967
00:40:26,496 --> 00:40:28,566
And they don't have to
have numbers associated

968
00:40:28,566 --> 00:40:31,156
with them yet, they'll be infer,
and here's how we do this.

969
00:40:31,306 --> 00:40:34,526
I know from just having, you
know, looked up some list

970
00:40:34,526 --> 00:40:36,806
of all the dorms on campus or
figure them out off the top

971
00:40:36,806 --> 00:40:38,736
of my head that here
all the dorms,

972
00:40:39,026 --> 00:40:40,916
feels like this is a good
candidate for an array.

973
00:40:41,006 --> 00:40:43,656
Otherwise, I'm gonna have to
copy and paste the same HTML

974
00:40:43,656 --> 00:40:45,226
for each of these
dorms so I can have

975
00:40:45,226 --> 00:40:47,386
that drop again and
again and again.

976
00:40:47,706 --> 00:40:50,646
So let me go ahead and declare
a variable called "dorms."

977
00:40:50,946 --> 00:40:53,556
I wrote it in all caps this
time just like you might in C

978
00:40:53,556 --> 00:40:55,246
to say this is some
global variable,

979
00:40:55,246 --> 00:40:56,466
this is a constant rather,

980
00:40:56,516 --> 00:40:59,266
this is a constant
storing all the values

981
00:40:59,266 --> 00:41:00,166
that aren't gonna change.

982
00:41:00,556 --> 00:41:04,786
In PHP, there's actually a
function called array whose

983
00:41:04,786 --> 00:41:06,726
purpose in life is
to take 1 or--

984
00:41:06,816 --> 00:41:10,376
0 or more arguments and those
arguments become the elements

985
00:41:10,426 --> 00:41:11,296
inside that array.

986
00:41:11,706 --> 00:41:14,106
So whereas in C, you would've
just done a curly brace.

987
00:41:14,266 --> 00:41:16,806
Unfortunately in PHP made the
slightly annoying decision

988
00:41:16,806 --> 00:41:19,956
to call it array as a function
and so you have parenthesis

989
00:41:20,246 --> 00:41:23,716
and then white space as
in C doesn't really matter

990
00:41:23,716 --> 00:41:27,516
and decided rather than having
this be a huge long line of text

991
00:41:27,516 --> 00:41:30,156
with commas and quotes, I
decided to put every dorm

992
00:41:30,156 --> 00:41:32,556
on its own line with
commas separating them just

993
00:41:32,556 --> 00:41:33,746
to keep things kind of pretty,

994
00:41:33,746 --> 00:41:35,976
but that's just an arbitrary
stylistic convention.

995
00:41:36,306 --> 00:41:37,936
But now notice what
I do down here.

996
00:41:38,176 --> 00:41:40,726
You can generate forms
even dynamically.

997
00:41:40,726 --> 00:41:42,296
So now notice what
I've done here.

998
00:41:42,546 --> 00:41:45,766
The TD tags are part
of the table.

999
00:41:46,076 --> 00:41:47,396
So TD is Table Data.

1000
00:41:47,656 --> 00:41:50,936
So ignore, for today's purposes,
some of the markup like TR

1001
00:41:50,936 --> 00:41:53,156
which is Table Row, TD
which is Table Data,

1002
00:41:53,436 --> 00:41:55,056
'cause like we saw last week,

1003
00:41:55,056 --> 00:41:57,276
that just let us structure
something behind the scenes.

1004
00:41:57,276 --> 00:41:58,466
And if it's new to you,

1005
00:41:58,736 --> 00:42:00,446
it actually is pretty
quick to pick up on.

1006
00:42:00,726 --> 00:42:01,886
But the point for now is this.

1007
00:42:02,346 --> 00:42:03,496
There is this other element,

1008
00:42:03,496 --> 00:42:06,486
for some reason it's not called
an input, it's called a select.

1009
00:42:06,876 --> 00:42:09,536
This is what the code with
which you make a drop-down menu

1010
00:42:09,566 --> 00:42:10,116
in HTML.

1011
00:42:10,536 --> 00:42:13,276
But notice, I can
commingle some PHP here, too.

1012
00:42:13,456 --> 00:42:16,046
I'm gonna say select
name equals dorm.

1013
00:42:16,046 --> 00:42:18,816
So this is declaring a
drop-down menu called "dorm,"

1014
00:42:19,056 --> 00:42:21,616
whose size is 1, which means
you're only gonna see one dorm

1015
00:42:21,616 --> 00:42:23,716
at a time which is
generally the default.

1016
00:42:24,116 --> 00:42:28,016
Notice that I wanted this
menu to be blank initially

1017
00:42:28,316 --> 00:42:30,916
so I declared an option
whose value is blank

1018
00:42:31,166 --> 00:42:34,306
and who has nothing inside
the open tag and close tag,

1019
00:42:34,486 --> 00:42:36,596
and that's how you just
create a blank option in one

1020
00:42:36,596 --> 00:42:38,776
of these drop-down menus
and then I have this.

1021
00:42:38,776 --> 00:42:40,306
And this is where
it gets interesting.

1022
00:42:40,686 --> 00:42:42,036
What's really nice about PHP is

1023
00:42:42,036 --> 00:42:44,836
that it doesn't just have
four loops in wild loops

1024
00:42:44,836 --> 00:42:47,516
and do wild loops, it has
some other useful mechanisms

1025
00:42:47,516 --> 00:42:48,846
that some of you might
have seen in Java

1026
00:42:48,846 --> 00:42:51,016
or other language
namely foreach.

1027
00:42:51,256 --> 00:42:52,906
Foreach is just a for loop.

1028
00:42:52,906 --> 00:42:55,426
It doesn't do anything
fundamentally new

1029
00:42:55,696 --> 00:42:58,196
but it allows you to write
some code a little more simply

1030
00:42:58,406 --> 00:43:01,056
and a little more quickly and
I can say something like this,

1031
00:43:01,456 --> 00:43:04,556
foreach array as variable.

1032
00:43:04,836 --> 00:43:05,856
So what do I mean by that?

1033
00:43:06,086 --> 00:43:09,346
Its first keyword inside
its pair of parenthesis is

1034
00:43:09,596 --> 00:43:11,226
to put the name of an array--

1035
00:43:11,496 --> 00:43:14,256
the variable for an array
in which case, dorms.

1036
00:43:14,496 --> 00:43:15,826
Then you literarily write as,

1037
00:43:15,826 --> 00:43:19,476
and then you choose any variable
name you want, dollar sign I,

1038
00:43:19,476 --> 00:43:22,406
dollar sign N, dollar
sign dorm in this case,

1039
00:43:22,406 --> 00:43:23,896
just to be conceptually
consistent.

1040
00:43:24,136 --> 00:43:26,236
And what's really neat
about this construct is

1041
00:43:26,236 --> 00:43:28,476
on every iteration
of this foreach loop,

1042
00:43:28,736 --> 00:43:32,406
it's going to assign to
this value the first element

1043
00:43:32,406 --> 00:43:35,346
in dorms; then on the next
iteration, the second element

1044
00:43:35,346 --> 00:43:37,546
in dorms; then on the
next iteration, the third

1045
00:43:37,546 --> 00:43:38,846
and so forth so you don't have

1046
00:43:38,846 --> 00:43:42,346
to do this very annoying
bracket dollar sign I notation

1047
00:43:42,346 --> 00:43:43,386
that we've been doing for weeks.

1048
00:43:43,626 --> 00:43:46,396
You can just conceptually loop
over all the elements in array

1049
00:43:46,396 --> 00:43:50,126
and assign each of them to
dollar sign dorm one at a time.

1050
00:43:50,416 --> 00:43:53,056
Now I need to dynamically
output this option element.

1051
00:43:53,336 --> 00:43:57,366
So notice what I'm doing
here, option value equals "".

1052
00:43:57,696 --> 00:44:00,736
But notice again, I'm
commingling PHP and HTML here

1053
00:44:00,986 --> 00:44:04,356
so I need to quickly drop into
PHP mode, output the value

1054
00:44:04,356 --> 00:44:07,556
of some variable, then
drop out of PHP mode

1055
00:44:07,556 --> 00:44:09,986
and so that's what I'm
doing, open bracket ?

1056
00:44:09,986 --> 00:44:13,106
equal sign which
says put the value

1057
00:44:13,106 --> 00:44:14,546
of the following variable here.

1058
00:44:14,546 --> 00:44:15,826
What variable?

1059
00:44:16,126 --> 00:44:20,226
Dorm, "". And then also because
the option element not unlike

1060
00:44:20,226 --> 00:44:23,786
hyper references has both
a value that you actually--

1061
00:44:23,786 --> 00:44:26,766
that actually get stored
like a URL and what you see.

1062
00:44:27,026 --> 00:44:28,706
I'm also just gonna
put verbatim,

1063
00:44:28,706 --> 00:44:31,196
the dorm's name out
here as well.

1064
00:44:31,196 --> 00:44:34,356
And so the end result if
we go to this example here,

1065
00:44:34,636 --> 00:44:37,596
froshims6.php, is
really the same form.

1066
00:44:37,596 --> 00:44:39,556
But now we're starting
to leverage some

1067
00:44:39,556 --> 00:44:41,626
of our program-- oh, dammit.

1068
00:44:41,626 --> 00:44:44,946
Now we're starting to leverage
some of our programming skills.

1069
00:44:44,976 --> 00:44:45,906
I'm gonna cheat and tell

1070
00:44:45,906 --> 00:44:47,846
that this is it 'cause I
already fixed this one.

1071
00:44:48,216 --> 00:44:50,976
And now we have this drop-down
whose first element is blank,

1072
00:44:51,046 --> 00:44:53,396
but then whose subsequent
elements actually have all

1073
00:44:53,396 --> 00:44:54,146
of these dorms.

1074
00:44:54,146 --> 00:44:55,896
And so here, too, is
where things start

1075
00:44:55,896 --> 00:44:57,666
to get even more
and more powerful.

1076
00:44:57,896 --> 00:45:01,256
Just to contextualize
this, something like--

1077
00:45:01,256 --> 00:45:03,366
I mean, frankly, even
something like Harvard FML

1078
00:45:03,366 --> 00:45:05,546
which is actually outsourced
to, I think, Tumblr,

1079
00:45:05,546 --> 00:45:07,216
which is a third party
blogging software.

1080
00:45:07,506 --> 00:45:10,356
They use some kind of database
and in that database are row

1081
00:45:10,356 --> 00:45:12,716
by row, all of the POSTs
that people have made.

1082
00:45:12,996 --> 00:45:15,296
If that site happens to
be implemented in PHP,

1083
00:45:15,296 --> 00:45:16,946
it doesn't have to
be, but maybe it is,

1084
00:45:17,136 --> 00:45:19,986
you can imagine getting back
an array of all of the POST

1085
00:45:19,986 --> 00:45:23,036
on Harvard FML and then just
using some fairly succinct

1086
00:45:23,186 --> 00:45:26,776
syntax like foreach POST as POST

1087
00:45:27,166 --> 00:45:29,996
and then this is how you
see the exact same structure

1088
00:45:29,996 --> 00:45:32,476
for everyone of the POST on
something like Harvard FML

1089
00:45:32,696 --> 00:45:33,956
but the content changes.

1090
00:45:33,956 --> 00:45:36,016
But it's really just being
generated by a for loop.

1091
00:45:36,016 --> 00:45:39,116
So much like we use for loops
in C to generate any kind

1092
00:45:39,116 --> 00:45:40,086
of cyclical structures,

1093
00:45:40,426 --> 00:45:45,556
similarly might we do
this here in PHP as well.

1094
00:45:45,626 --> 00:45:50,066
So let me go ahead and spoil
just a couple of more details

1095
00:45:51,006 --> 00:45:56,846
and show us the most fun one
which is going to be this one.

1096
00:45:56,896 --> 00:46:00,676
Alright, so froshims8.php,

1097
00:46:01,076 --> 00:46:03,136
we finally have--
alright, there we go.

1098
00:46:03,136 --> 00:46:04,756
This one is clean.

1099
00:46:04,786 --> 00:46:07,686
In froshims8.php, notice
that it actually submits

1100
00:46:08,026 --> 00:46:11,326
to a file called register8.php.

1101
00:46:11,326 --> 00:46:13,576
And-- I don't actually have
eight versions of registration.

1102
00:46:13,576 --> 00:46:14,806
I just wanted the
numbers to line up,

1103
00:46:14,856 --> 00:46:16,116
if you're following
along on paper.

1104
00:46:16,366 --> 00:46:18,856
So this form looks exactly
the same as every other,

1105
00:46:19,086 --> 00:46:21,096
but it submits to register8.php.

1106
00:46:21,226 --> 00:46:25,066
'Cause I got tired being the
proctor of dealing with all

1107
00:46:25,066 --> 00:46:27,596
of these emails, so now I
actually wanna store this

1108
00:46:27,596 --> 00:46:28,876
information in a database.

1109
00:46:28,986 --> 00:46:31,676
So I'll look back at the code
in a moment, but let's go ahead

1110
00:46:31,676 --> 00:46:33,406
and introduce the
actual database

1111
00:46:33,406 --> 00:46:34,286
in which we'll store this.

1112
00:46:34,626 --> 00:46:36,826
So a database is really just--

1113
00:46:37,166 --> 00:46:39,366
a database as most people
know it is what's called a

1114
00:46:39,366 --> 00:46:40,446
relational database.

1115
00:46:40,526 --> 00:46:43,896
And a relational database
is essentially some kind

1116
00:46:43,896 --> 00:46:46,856
of special server software
that stores lots of tables.

1117
00:46:46,856 --> 00:46:48,936
And a table is just something
with rows and columns.

1118
00:46:48,936 --> 00:46:52,546
It's just a spreadsheet for-- if
that's the most familiar notion.

1119
00:46:52,886 --> 00:46:55,616
So there exist various
implementations of this idea

1120
00:46:55,616 --> 00:46:58,186
of a database, there
exist Microsoft Access,

1121
00:46:58,186 --> 00:47:00,356
Microsoft SQL Server, Oracle,

1122
00:47:00,546 --> 00:47:03,866
and then something called
MySQL, and dozens of others.

1123
00:47:03,896 --> 00:47:06,356
But MySQL is one of
the most popular, free,

1124
00:47:06,426 --> 00:47:09,026
open source database servers.

1125
00:47:09,026 --> 00:47:11,416
And by open source, that means
you can look at the source code

1126
00:47:11,416 --> 00:47:13,546
that other people have
written and it power

1127
00:47:13,546 --> 00:47:14,816
such sites as Facebook.

1128
00:47:14,856 --> 00:47:15,776
Frankly, it was Facebook--

1129
00:47:15,776 --> 00:47:18,806
was really one of its biggest
proponents in recent years

1130
00:47:18,806 --> 00:47:22,486
that really pushing it to its
limits in terms of scalability

1131
00:47:22,486 --> 00:47:24,526
and they still use it
for much of their data.

1132
00:47:24,526 --> 00:47:27,416
So what better option
is there when it's free

1133
00:47:27,636 --> 00:47:29,976
and apparently it
scales pretty darn well?

1134
00:47:29,976 --> 00:47:32,976
So we too, because of
its relative ease of use

1135
00:47:32,976 --> 00:47:35,566
and its free availability,
use MySQL for this portion

1136
00:47:35,566 --> 00:47:37,476
of the course, which is to
say that we, the course,

1137
00:47:37,726 --> 00:47:40,116
run a database server and
what's neat is you can go

1138
00:47:40,116 --> 00:47:42,486
on your own laptop and
download the same software

1139
00:47:42,486 --> 00:47:44,186
and run a database
on your laptop.

1140
00:47:44,506 --> 00:47:45,706
I'm sorry, that's not useful

1141
00:47:45,706 --> 00:47:48,206
for other people 'cause your
laptop is probably not a web

1142
00:47:48,206 --> 00:47:49,206
server on the internet.

1143
00:47:49,446 --> 00:47:51,176
So generally, when you
have a database server,

1144
00:47:51,176 --> 00:47:53,746
it leaves on some central
server, like the cloud.

1145
00:47:53,746 --> 00:47:55,696
If you decide to commercialize

1146
00:47:55,696 --> 00:47:57,466
or just migrate your
final projects though off

1147
00:47:57,466 --> 00:47:59,366
to a commercial web host
at the end of the semester,

1148
00:47:59,596 --> 00:48:00,956
almost every commercial web POST

1149
00:48:00,956 --> 00:48:03,316
out there these days
provides MySQL server.

1150
00:48:03,316 --> 00:48:05,196
So it's very easy to
run your data elsewhere.

1151
00:48:05,566 --> 00:48:06,886
So what does this actually mean?

1152
00:48:06,886 --> 00:48:08,376
Well, I need at some way

1153
00:48:08,646 --> 00:48:10,746
of actually creating
these things called tables

1154
00:48:10,806 --> 00:48:12,386
in the course's database server.

1155
00:48:12,616 --> 00:48:15,046
And for this, something
like this froshims feels

1156
00:48:15,046 --> 00:48:17,296
like I just need one
table, one spreadsheet,

1157
00:48:17,516 --> 00:48:20,956
each of whose columns are gonna
name and then a captain column

1158
00:48:20,996 --> 00:48:23,776
and a gender column, and a dorm
column, and that's about it.

1159
00:48:23,976 --> 00:48:26,906
So if you were to pull up Google
Docs or Google Spreadsheets

1160
00:48:26,906 --> 00:48:28,836
or Excel, you would
just write those labels

1161
00:48:28,836 --> 00:48:29,816
at the top of the field.

1162
00:48:29,816 --> 00:48:32,516
But because we're actually using
this in a programing context,

1163
00:48:32,776 --> 00:48:34,196
I'm actually gonna
pull up this tool.

1164
00:48:34,796 --> 00:48:39,826
So there is a program that
leaves per Problem Set 7

1165
00:48:39,826 --> 00:48:43,116
at cloud.cs50.net/phpmyadmin.

1166
00:48:43,226 --> 00:48:46,636
It's actually coincidence that
the thing is called phpmyadmin.

1167
00:48:46,906 --> 00:48:48,446
It does happen to be in--

1168
00:48:48,446 --> 00:48:50,346
written in PHP but
we're using it

1169
00:48:50,346 --> 00:48:53,516
because it's a wonderful
user-friendly web-based GUI

1170
00:48:53,766 --> 00:48:55,586
for interacting with
a database server.

1171
00:48:55,586 --> 00:48:58,116
So when you pull up this
URL, you're prompted to login

1172
00:48:58,116 --> 00:49:00,856
with a username and password,
pset7 will tell you exactly what

1173
00:49:00,856 --> 00:49:03,556
that username and password are
and you'll see this interface.

1174
00:49:03,556 --> 00:49:05,496
And frankly, this is a
little overwhelming at first

1175
00:49:05,706 --> 00:49:06,496
but almost everything

1176
00:49:06,496 --> 00:49:08,976
on the right hand side we
can ignore from now on.

1177
00:49:08,976 --> 00:49:11,986
Because the only I care about at
the moment is the fact that now

1178
00:49:11,986 --> 00:49:14,676
that I've logged in, I
have access to a database

1179
00:49:14,796 --> 00:49:17,316
that we've created for
you all and mine happens

1180
00:49:17,316 --> 00:49:19,356
to be called Malan_Lecture.

1181
00:49:19,436 --> 00:49:21,606
Yours will be called
Username_pset7.

1182
00:49:21,606 --> 00:49:23,286
So I'm gonna click this.

1183
00:49:23,286 --> 00:49:26,296
And now notice, no
tables found in database.

1184
00:49:26,406 --> 00:49:28,776
So this is what would happen
too in a commercial web host

1185
00:49:28,776 --> 00:49:30,766
or if you install the
software on your own laptop,

1186
00:49:30,986 --> 00:49:34,706
you would initially have no
actual tables in your database.

1187
00:49:35,036 --> 00:49:37,366
So you can think of table
really as a worksheet,

1188
00:49:37,506 --> 00:49:39,766
like a spreadsheet has
multiple worksheets in Excel

1189
00:49:39,766 --> 00:49:42,896
and Google Docs, so I have
no tables yet, so I need one.

1190
00:49:42,926 --> 00:49:45,486
So I'm gonna create one
called registrants, let's say,

1191
00:49:45,596 --> 00:49:46,886
for all the people
who have registered,

1192
00:49:47,146 --> 00:49:49,796
and then how many fields,
quick sanity check for,

1193
00:49:49,796 --> 00:49:53,936
so then I'm gonna click go and
realize there are different ways

1194
00:49:53,936 --> 00:49:55,576
of interacting with
a database server.

1195
00:49:55,766 --> 00:49:58,986
This is just one free user
friendly way of doing it.

1196
00:49:59,346 --> 00:50:00,976
So now you'll see on
the page that appears.

1197
00:50:01,046 --> 00:50:03,236
>> It's kind of wide
on my screen here.

1198
00:50:03,466 --> 00:50:06,636
But I'm being asked for a
few answers to questions.

1199
00:50:06,696 --> 00:50:08,556
First, I'm being asked to answer

1200
00:50:08,716 --> 00:50:10,156
"What do you want me
to call this field?"

1201
00:50:10,256 --> 00:50:11,846
So I'm gonna quickly
say name field.

1202
00:50:12,226 --> 00:50:15,936
This one is going to be, let's
see, what was it, captain.

1203
00:50:16,376 --> 00:50:18,106
This next one is
gonna be gender.

1204
00:50:18,106 --> 00:50:19,876
And this last one
is going to be dorm.

1205
00:50:19,876 --> 00:50:22,266
But there're a few other
questions I need to answer.

1206
00:50:22,606 --> 00:50:27,066
Unlike PHP which doesn't really
have explicit data types,

1207
00:50:27,066 --> 00:50:29,026
at least that you need to
mention, it's a little more

1208
00:50:29,026 --> 00:50:31,956
like C MySQL because when
you're using a database,

1209
00:50:32,216 --> 00:50:34,326
it's actually really
useful to know what type

1210
00:50:34,326 --> 00:50:36,476
of data you're storing
for performance reasons.

1211
00:50:36,476 --> 00:50:38,756
Now for our example here,
there's never gonna be more

1212
00:50:38,756 --> 00:50:40,586
than like 1600 freshman
register,

1213
00:50:40,856 --> 00:50:43,086
but again consider Facebook,
consider Google Docs,

1214
00:50:43,086 --> 00:50:45,826
consider any concepts where
there's actually thousands

1215
00:50:45,826 --> 00:50:47,806
of entries or millions
of entries.

1216
00:50:48,076 --> 00:50:50,706
In fact, we've been running
some of those CS50 apps now

1217
00:50:50,706 --> 00:50:53,026
that you-- you might have played
with this semester for two

1218
00:50:53,026 --> 00:50:56,656
or three years and some of
those databases case and points,

1219
00:50:57,526 --> 00:51:01,276
if we go to tweets.cs50.net,
we have a MySQL table

1220
00:51:01,276 --> 00:51:06,476
that stores all the tweets and
right now it has 105,654 tweets

1221
00:51:06,546 --> 00:51:09,846
that people have tweeted
just in a row in a database

1222
00:51:09,846 --> 00:51:11,506
and that's not even
considered that big.

1223
00:51:11,506 --> 00:51:13,756
So you can actually do some
neat things with the software

1224
00:51:13,916 --> 00:51:14,896
but we need to choose a type.

1225
00:51:14,946 --> 00:51:17,716
Now for a name, we want
a string conceptually.

1226
00:51:17,946 --> 00:51:19,846
But in MySQL, there's
different type of strings

1227
00:51:19,846 --> 00:51:21,356
but we'll highlight
just one for now,

1228
00:51:21,626 --> 00:51:23,726
VARCHAR is perhaps
the most common.

1229
00:51:23,726 --> 00:51:26,036
VARCHAR is variable
char and this is

1230
00:51:26,036 --> 00:51:28,316
when you know you want
a string of characters

1231
00:51:28,456 --> 00:51:31,136
but you're not quite sure how
long that string is gonna be

1232
00:51:31,296 --> 00:51:34,206
but MySQL does demand that
you give it an upper bound.

1233
00:51:34,356 --> 00:51:37,286
So very common for name
might be, how many let--

1234
00:51:37,286 --> 00:51:39,946
characters do we need to
allow for a person's name.

1235
00:51:41,076 --> 00:51:44,766
I mean like 10 is feels too
short, 20 feels like it's short,

1236
00:51:44,766 --> 00:51:46,496
I mean frankly there's
not that much harm

1237
00:51:46,496 --> 00:51:47,956
in just rounding up, frankly.

1238
00:51:47,956 --> 00:51:51,396
So let's say 255 is a
pretty good upper bound even

1239
00:51:51,396 --> 00:51:53,406
for certain foreign names
which might be longer

1240
00:51:53,406 --> 00:51:54,586
than traditional American names

1241
00:51:54,586 --> 00:51:56,116
like that gives us
a pretty good buffer

1242
00:51:56,116 --> 00:51:59,616
but we could go even higher,
thousand and 24, you know,

1243
00:51:59,616 --> 00:52:01,496
generally people have rules
of thumb that they stick to,

1244
00:52:01,496 --> 00:52:05,446
255 is a popular
convention because years ago,

1245
00:52:05,446 --> 00:52:08,626
this actually used to be the
maximum though now it's 65,000

1246
00:52:08,626 --> 00:52:10,866
characters, that's probably
overkill for someone's name.

1247
00:52:11,246 --> 00:52:12,366
Now what about captain?

1248
00:52:12,646 --> 00:52:14,186
So how do you implement
the notion of a captain,

1249
00:52:15,146 --> 00:52:17,106
what data type instinctively
might you want?

1250
00:52:17,926 --> 00:52:18,676
So a Boolean.

1251
00:52:18,676 --> 00:52:20,656
So it turns out that MySQL

1252
00:52:20,836 --> 00:52:24,336
and generally SQL databases
might not support Booleans per

1253
00:52:24,336 --> 00:52:26,316
se but they can mimic them.

1254
00:52:26,316 --> 00:52:29,216
In fact even if we see it
here, let me scroll back up,

1255
00:52:29,416 --> 00:52:31,256
there is a Boolean value there

1256
00:52:31,706 --> 00:52:34,726
but you can actually implement a
Boolean frankly with just an int

1257
00:52:35,026 --> 00:52:37,346
or short or 8-- or char frankly

1258
00:52:37,556 --> 00:52:39,336
so that's actually what the
database server is doing.

1259
00:52:39,336 --> 00:52:41,146
It's calling it a
Boolean but to be honest,

1260
00:52:41,146 --> 00:52:43,476
this is probably gonna
cost us at least 8 bits.

1261
00:52:43,886 --> 00:52:46,666
It's just the computers
deal usually with bytes,

1262
00:52:46,696 --> 00:52:48,406
not individual bits,
so that's fine.

1263
00:52:48,496 --> 00:52:49,816
Now captain is gonna
be a Boolean.

1264
00:52:50,056 --> 00:52:52,616
Gender, meanwhile, I actually
have a few options here.

1265
00:52:52,616 --> 00:52:54,616
So I could do something
like another Boolean

1266
00:52:54,616 --> 00:52:57,006
and I could rename
gender to be female

1267
00:52:57,006 --> 00:52:58,696
and then it can just
be true or false

1268
00:52:58,696 --> 00:53:00,426
or could be male and
be false or true.

1269
00:53:00,606 --> 00:53:02,726
I could do something like
an int and just assume

1270
00:53:02,726 --> 00:53:06,436
that 0 is female, 1 is
male, I could do a string

1271
00:53:06,436 --> 00:53:10,056
and actually store M or F, I
could store male or female.

1272
00:53:10,316 --> 00:53:11,936
Frankly, there's so
many different ways.

1273
00:53:11,966 --> 00:53:15,346
Let's go ahead here and let's
just leave it as, let's say,

1274
00:53:15,346 --> 00:53:17,666
let's just do 255 again
'cause we won't think

1275
00:53:17,666 --> 00:53:19,536
about it too hard here but
it's gonna be a string.

1276
00:53:19,536 --> 00:53:21,546
We'll store male or female
or something like that

1277
00:53:21,676 --> 00:53:23,076
but it might not be
the best decision

1278
00:53:23,166 --> 00:53:24,446
but it will get the
job done for now.

1279
00:53:24,676 --> 00:53:27,106
And then dorm, this
probably should be a VARCHAR

1280
00:53:27,106 --> 00:53:28,466
and we'll say 255.

1281
00:53:28,466 --> 00:53:32,216
But again, we're not using
255 bytes necessarily.

1282
00:53:32,436 --> 00:53:33,956
It will use a variable number.

1283
00:53:33,956 --> 00:53:35,316
This is just an upper bound.

1284
00:53:35,516 --> 00:53:37,106
Now finally if I
scroll over here,

1285
00:53:37,106 --> 00:53:38,356
you're asked a few
more questions

1286
00:53:38,356 --> 00:53:39,796
which eventually
become relevant.

1287
00:53:39,966 --> 00:53:42,016
Do you want this thing
to have a default value?

1288
00:53:42,076 --> 00:53:43,806
For instance, do you
want it to be null,

1289
00:53:43,806 --> 00:53:46,616
do you want everybody's
default name to be John Harvard?

1290
00:53:46,616 --> 00:53:49,136
You could do that at the
database level by typing

1291
00:53:49,136 --> 00:53:51,976
into this field but for
now I'm just gonna go ahead

1292
00:53:51,976 --> 00:53:53,726
and click save.

1293
00:53:53,816 --> 00:53:56,996
And now notice I'm
returned to this tab here.

1294
00:53:56,996 --> 00:53:58,936
This is the so-called
structure tab

1295
00:53:59,176 --> 00:54:01,356
and now you just see a
little reminder of all

1296
00:54:01,356 --> 00:54:03,816
of the fields you just
created, their default types

1297
00:54:03,816 --> 00:54:06,156
and then only because MySQL
was originally written

1298
00:54:06,156 --> 00:54:09,056
by some Swedes, the
default coalition is--

1299
00:54:09,206 --> 00:54:11,716
refers to Swedish,
it's not a problem.

1300
00:54:11,716 --> 00:54:15,386
You can fit all the
American characters inside

1301
00:54:15,386 --> 00:54:16,806
of the same encoding scheme.

1302
00:54:16,806 --> 00:54:19,146
So it's not a bug,
it's a feature.

1303
00:54:19,176 --> 00:54:21,446
They wrote it, they get to
decide the default encoding.

1304
00:54:21,646 --> 00:54:22,776
So what's now the takeaway?

1305
00:54:22,776 --> 00:54:25,956
Well let me go back to
froshims8 and register8.

1306
00:54:26,386 --> 00:54:29,226
Notice now I have the following
code and I'll just tease you

1307
00:54:29,226 --> 00:54:31,256
with some of it first then
we'll look at more detail.

1308
00:54:31,636 --> 00:54:33,196
It turns out there's
a function called

1309
00:54:33,256 --> 00:54:36,036
"mysql_connect" that's using
my very public user name

1310
00:54:36,036 --> 00:54:36,856
and password now.

1311
00:54:37,146 --> 00:54:39,736
I then have a function called
"mysql_select_database"

1312
00:54:39,786 --> 00:54:41,766
because there's gonna
be hundreds of databases

1313
00:54:41,766 --> 00:54:45,146
on this server, I wanna select
just mine called Malan_Lecture

1314
00:54:45,536 --> 00:54:47,766
then there's gonna be some
code down here where I'm going

1315
00:54:47,766 --> 00:54:49,666
to scrub the user's input.

1316
00:54:49,826 --> 00:54:52,206
It turns out there's a lot
of bad things people can do

1317
00:54:52,206 --> 00:54:54,376
by knowing this language
we're about to look

1318
00:54:54,376 --> 00:54:57,796
at called SQL whereby they
can log into your website,

1319
00:54:57,796 --> 00:54:59,966
they can delete your data if
they know what they're doing.

1320
00:55:00,216 --> 00:55:01,936
But the real magic
boils down to this.

1321
00:55:02,456 --> 00:55:03,636
Instead of sending an email,

1322
00:55:03,956 --> 00:55:06,986
I'm ultimately gonna call a
function called mysql_query

1323
00:55:07,256 --> 00:55:09,806
whose purpose in life is to
take a query which will right

1324
00:55:09,806 --> 00:55:12,446
in a moment store that
data not in an email

1325
00:55:12,446 --> 00:55:14,026
but into that database.

1326
00:55:14,026 --> 00:55:16,366
So now, if I've done
all this correctly,

1327
00:55:16,616 --> 00:55:21,506
I can visit froshims8.php,
I can say David Malan

1328
00:55:21,686 --> 00:55:25,526
and will be a captain, gender
and we'll say Matthew's

1329
00:55:25,596 --> 00:55:29,976
and click register and it says
you are registered really,

1330
00:55:30,156 --> 00:55:30,896
that's means nothing.

1331
00:55:31,226 --> 00:55:32,866
So now let me go
back to my database

1332
00:55:33,506 --> 00:55:34,576
which the proctor could do

1333
00:55:34,576 --> 00:55:37,056
or frankly I probably make a
more user-friendly interphase

1334
00:55:37,056 --> 00:55:39,296
with proctor, I being the
programmer don't mind so much.

1335
00:55:39,326 --> 00:55:44,406
I'm gonna click browse and, wow,
I now have stored in my table,

1336
00:55:44,466 --> 00:55:46,166
my spreadsheet, now this record,

1337
00:55:46,206 --> 00:55:48,206
which means now I can do
anything I want with this data,

1338
00:55:48,206 --> 00:55:51,216
I can email it out later, I
can render it on a website,

1339
00:55:51,496 --> 00:55:59,906
I can search it, sort it, more
on that after a 5-minute break.

1340
00:56:00,386 --> 00:56:02,346
Alright, so we are back.

1341
00:56:02,346 --> 00:56:04,456
That was enough time
for me to fix my bug.

1342
00:56:04,456 --> 00:56:07,106
I forgot how to compute
percents so

1343
00:56:07,376 --> 00:56:08,776
and I also forgot how to sort.

1344
00:56:09,176 --> 00:56:11,226
So both bugs had been fixed much

1345
00:56:11,376 --> 00:56:14,656
to my disappointment though
thankfully Ben, Joseph,

1346
00:56:14,656 --> 00:56:17,256
and Brook [phonetic] have pulled
behind me in the leadings.

1347
00:56:17,606 --> 00:56:22,166
I am now back at 0 percent, rank
number 15 here since my stock,

1348
00:56:22,166 --> 00:56:25,646
my penny stocks have probably
gone back up but Michael

1349
00:56:25,646 --> 00:56:27,336
and Zack [phonetic]
are doing pretty well.

1350
00:56:27,336 --> 00:56:30,326
They are now up 200 and
100 percent respectively,

1351
00:56:30,616 --> 00:56:32,216
so good luck.

1352
00:56:32,216 --> 00:56:34,696
Inevitably, this turns
out to be not so much.

1353
00:56:34,696 --> 00:56:37,336
He was really good in investing
at Harvard but who's really good

1354
00:56:37,336 --> 00:56:38,816
about leveraging
certain weaknesses

1355
00:56:38,816 --> 00:56:42,806
in the big board namely that
one comes to mind, not to spoil.

1356
00:56:42,976 --> 00:56:43,716
We'll spoil this.

1357
00:56:44,086 --> 00:56:46,026
We'll give you guys the
edge and for those not here,

1358
00:56:46,026 --> 00:56:46,806
they won't know this trick.

1359
00:56:47,296 --> 00:56:50,266
So it turns out that if stock
quotes are not realtime,

1360
00:56:51,136 --> 00:56:53,506
and there are something
like Yahoo!

1361
00:56:53,506 --> 00:56:57,716
Finance, but other stock quotes
are realtime unlike Bloomberg TV

1362
00:56:57,716 --> 00:56:59,886
or CNN or your own
E-Trade account,

1363
00:57:00,186 --> 00:57:02,026
turns out that you
can effectively see

1364
00:57:02,026 --> 00:57:03,836
into the future by
about 15 minutes.

1365
00:57:04,386 --> 00:57:07,096
So if you are in fact
watching certain penny stocks

1366
00:57:08,616 --> 00:57:12,586
and realize, wow,
that stock just shut

1367
00:57:12,586 --> 00:57:16,096
up on my real E-Trade account,
still have about 15 minutes

1368
00:57:16,096 --> 00:57:17,776
to scoop up as many
shares as you can

1369
00:57:18,126 --> 00:57:21,116
on the CS50 finance
version of it.

1370
00:57:21,116 --> 00:57:23,606
Also too, with a lot
of these penny stocks,

1371
00:57:23,606 --> 00:57:25,056
actually I don't mind
just divulging this

1372
00:57:25,056 --> 00:57:26,906
because inevitably every
semester, there is some student

1373
00:57:26,906 --> 00:57:28,616
who thinks here she's
really being clever

1374
00:57:28,616 --> 00:57:30,926
in gaming the system when really
we're not just telling you

1375
00:57:30,926 --> 00:57:31,706
about these weaknesses.

1376
00:57:31,706 --> 00:57:32,676
And now I pull the disclosure.

1377
00:57:32,676 --> 00:57:35,296
Let's see if we can really
push the maximum amount

1378
00:57:35,296 --> 00:57:37,556
of money earned in
three weeks' time up.

1379
00:57:37,626 --> 00:57:39,416
The other weakness of
course is if you're buying

1380
00:57:39,416 --> 00:57:44,006
like 10,000 shares or 100,000
shares of some penny stock

1381
00:57:44,006 --> 00:57:46,496
in our simulator here,
probably in the real world,

1382
00:57:46,556 --> 00:57:48,836
you yourself are gonna
drive the price way up

1383
00:57:48,966 --> 00:57:50,006
and so you're not
gonna actually get

1384
00:57:50,006 --> 00:57:51,276
that penny stock for a penny.

1385
00:57:51,326 --> 00:57:53,466
So realize that there-- you
gotta take some of these

1386
00:57:53,466 --> 00:57:56,386
with a grain of salt but what's
neat is you can actually see

1387
00:57:56,386 --> 00:57:57,466
what each other are doing.

1388
00:57:57,466 --> 00:57:59,046
If you'd like to learn
just how good they are

1389
00:57:59,046 --> 00:58:00,426
or just how clever
they're being.

1390
00:58:00,786 --> 00:58:04,156
For instance Michael has really
been an active day trader here

1391
00:58:04,156 --> 00:58:07,266
in the one day this is
available playing with our--

1392
00:58:07,266 --> 00:58:10,806
actually not some
terribly cheap stocks.

1393
00:58:10,896 --> 00:58:14,126
So perhaps he has some
ability to see into the future.

1394
00:58:14,126 --> 00:58:17,656
I just went with one penny
stock at 41 cents there.

1395
00:58:17,656 --> 00:58:18,516
I'm gonna hang on to it.

1396
00:58:18,516 --> 00:58:21,776
I'm a long term investor
with these penny stocks.

1397
00:58:22,006 --> 00:58:23,166
[Laughter] So in any case,

1398
00:58:23,166 --> 00:58:26,106
how do we actually now
start storing this data just

1399
00:58:26,106 --> 00:58:27,776
like the data you're
seeing now on the big board

1400
00:58:27,976 --> 00:58:29,266
into an actual database.

1401
00:58:29,266 --> 00:58:31,256
Well it turns out the
magic there derives

1402
00:58:31,256 --> 00:58:33,996
from a language called SQL,
Structured Query Language.

1403
00:58:34,306 --> 00:58:36,936
This is not so much a
programming language

1404
00:58:36,936 --> 00:58:38,426
as it is as the cue denotes.

1405
00:58:38,676 --> 00:58:41,256
A query language whereby
if you have a database

1406
00:58:41,256 --> 00:58:44,286
and you wanna grab data from
that database, you need some way

1407
00:58:44,286 --> 00:58:46,016
of expressing it and it turns

1408
00:58:46,016 --> 00:58:49,126
out you can do most
database manipulations

1409
00:58:49,126 --> 00:58:50,996
with just four basic commands.

1410
00:58:50,996 --> 00:58:53,176
One is Insert and we
actually used that already

1411
00:58:53,176 --> 00:58:55,876
and we'll pull back that
layer in a moment of my code.

1412
00:58:56,106 --> 00:58:58,466
Select if you wanna grab
data from the database.

1413
00:58:58,546 --> 00:59:00,176
Update if you just
wanna tweet something.

1414
00:59:00,426 --> 00:59:02,456
And Delete if you wanna
delete from the database.

1415
00:59:02,456 --> 00:59:04,376
And there are a bunch
of other statements

1416
00:59:04,376 --> 00:59:07,096
that you can actually get in
SQL but these are probably

1417
00:59:07,096 --> 00:59:10,046
by far the most common and
certainly the most useful

1418
00:59:10,046 --> 00:59:13,296
to learn right up at--
right at from the get-go.

1419
00:59:13,556 --> 00:59:15,086
So let's go ahead
and take a look here.

1420
00:59:15,086 --> 00:59:18,716
So if I go back into this
very last froshims example,

1421
00:59:19,056 --> 00:59:21,936
you will see in froshims--

1422
00:59:22,176 --> 00:59:25,006
in register8 that I
did the following.

1423
00:59:25,086 --> 00:59:27,736
At the very top of the file,
first I have my sanity check.

1424
00:59:27,846 --> 00:59:30,526
If name is blank or gender
is blank or dorm is blank,

1425
00:59:30,796 --> 00:59:33,136
redirect the user to
this location which is

1426
00:59:33,136 --> 00:59:35,676
that long URL just 'cause I put
a lot of subdirectories there

1427
00:59:35,946 --> 00:59:37,776
but in other words get them out
of here, like send them back

1428
00:59:37,776 --> 00:59:39,456
to the form and let
them resubmit.

1429
00:59:39,666 --> 00:59:41,056
This isn't the most
user friendly form.

1430
00:59:41,056 --> 00:59:41,976
There's no feedback here.

1431
00:59:41,976 --> 00:59:43,836
So realize each of these
examples should be looked

1432
00:59:43,926 --> 00:59:44,716
in isolation.

1433
00:59:44,966 --> 00:59:46,966
Sometimes we have read
texting, there's an error,

1434
00:59:46,966 --> 00:59:47,956
sometimes we don't bother.

1435
00:59:48,216 --> 00:59:50,986
Each of these examples is meant
to illustrate per the comments

1436
00:59:50,986 --> 00:59:52,426
to top each a different point.

1437
00:59:52,656 --> 00:59:55,526
But let's supposed that
we passed the validation.

1438
00:59:55,526 --> 00:59:58,246
In other words the user has not
left any of those fields blank

1439
00:59:58,536 --> 01:00:00,256
so we don't execute this branch

1440
01:00:00,256 --> 01:00:01,826
and so we reach this
line of code.

1441
01:00:02,066 --> 01:00:03,666
>> It turns out that
if you wanna connect

1442
01:00:03,666 --> 01:00:07,676
to a MySQL database in PHP code,
it's very simple and realize

1443
01:00:07,676 --> 01:00:09,736
that MySQL is not
at all tied to PHP.

1444
01:00:09,736 --> 01:00:12,386
You can connect to it in
Java, in C, in C plus plus,

1445
01:00:12,386 --> 01:00:15,636
in C sharp, really any of your
favorite languages you can use

1446
01:00:15,906 --> 01:00:17,686
to connect to this
type of database.

1447
01:00:17,686 --> 01:00:18,546
And so that's nice.

1448
01:00:18,546 --> 01:00:20,846
We're really not tying our
hands with one language here.

1449
01:00:21,216 --> 01:00:22,696
So how do you connect
to a database?

1450
01:00:23,336 --> 01:00:24,906
Well, I read the
manual and found

1451
01:00:24,906 --> 01:00:26,656
that there's a function
called mysql_connect

1452
01:00:26,656 --> 01:00:27,886
and it takes three arguments.

1453
01:00:28,026 --> 01:00:32,466
One, the IP address or the
domain name of the server

1454
01:00:32,466 --> 01:00:34,986
to which you want to connect, as
you'll see in the problems set

1455
01:00:34,986 --> 01:00:39,096
and in your distribution code,
mysql.local domain is the made

1456
01:00:39,096 --> 01:00:42,156
up domain name that we created
for our database server.

1457
01:00:42,386 --> 01:00:44,986
And I say made up because we
don't want this database server

1458
01:00:44,986 --> 01:00:46,606
out there in the
internet for other people

1459
01:00:46,606 --> 01:00:48,066
to connect to and interact with.

1460
01:00:48,066 --> 01:00:50,796
We want it just to be private
to us on the cloud so we came

1461
01:00:50,796 --> 01:00:53,416
out with this local
domain moniker instead

1462
01:00:53,416 --> 01:00:55,116
of using .com or .edu.

1463
01:00:55,116 --> 01:00:56,716
It's only accessible
within the Cloud.

1464
01:00:57,046 --> 01:00:59,126
Now it takes my user name
as my second argument.

1465
01:00:59,386 --> 01:01:03,156
My password as my third argument
and then I now have a connection

1466
01:01:03,156 --> 01:01:05,296
to that database assuming
everything was correct

1467
01:01:05,296 --> 01:01:08,296
and so now I have to select the
specific database because again,

1468
01:01:08,296 --> 01:01:11,146
there's like 500
databases on this server.

1469
01:01:11,276 --> 01:01:13,116
I wanna choose specifically
my own

1470
01:01:13,116 --> 01:01:14,826
which in this case it's
called Malan_Lecture.

1471
01:01:15,076 --> 01:01:17,796
Yours again will be
called JHarvard_pset7

1472
01:01:17,976 --> 01:01:18,716
or something like that.

1473
01:01:19,206 --> 01:01:21,576
Now notice this and I've
comment to the codes

1474
01:01:21,576 --> 01:01:22,596
to make clear what's going on.

1475
01:01:22,596 --> 01:01:25,006
There're not many lines of
codes required to get data

1476
01:01:25,006 --> 01:01:27,486
into a database, pretty much
the same number as everybody

1477
01:01:27,486 --> 01:01:28,496
as required to make an email.

1478
01:01:29,016 --> 01:01:30,186
So scrub inputs.

1479
01:01:30,186 --> 01:01:34,036
So this is actually a good habit
to get in to very early on.

1480
01:01:34,036 --> 01:01:36,236
There is what's known in
the world something called a

1481
01:01:36,236 --> 01:01:37,396
"SQL injection attack."

1482
01:01:37,946 --> 01:01:39,206
This essentially is an attack

1483
01:01:39,576 --> 01:01:42,616
where by a sufficiently clever
adversary goes to your web page

1484
01:01:42,616 --> 01:01:45,936
which has some kind of HTML form
and instead of typing in David

1485
01:01:45,936 --> 01:01:50,416
to the form and instead of
typing in any expected text

1486
01:01:50,606 --> 01:01:53,436
into that form, instead this
adversary starts tossing

1487
01:01:53,436 --> 01:01:55,266
in weird characters
like maybe some quotes,

1488
01:01:55,266 --> 01:01:58,796
maybe some semicolons,
maybe the keyword delete.

1489
01:01:58,796 --> 01:02:00,996
The whole idea of
being they're trying

1490
01:02:00,996 --> 01:02:04,446
to insert dangerous
commands into your database

1491
01:02:04,446 --> 01:02:06,866
without you realizing it
so that you might be trick

1492
01:02:06,866 --> 01:02:08,076
into executing this code.

1493
01:02:08,276 --> 01:02:10,856
We'll talk more about
this in due time perhaps.

1494
01:02:11,106 --> 01:02:15,886
But for now, know that anytime
you insert data into a database

1495
01:02:15,886 --> 01:02:17,476
that was handed to
you by a user,

1496
01:02:17,726 --> 01:02:19,886
you should call this
idiotically named function.

1497
01:02:20,376 --> 01:02:25,656
Frankly,
mysql_real_escape_string,

1498
01:02:26,016 --> 01:02:27,746
so 0 point for style
there, frankly.

1499
01:02:28,026 --> 01:02:30,746
But that's what we're
stock with.

1500
01:02:30,746 --> 01:02:32,916
That function's purpose
in life is essentially

1501
01:02:32,916 --> 01:02:35,666
to put backslashes in front of
any of those scary characters

1502
01:02:35,696 --> 01:02:37,396
like semicolons and
quotes, they're just

1503
01:02:37,396 --> 01:02:39,956
in general had caused us
a little bit of concern

1504
01:02:39,956 --> 01:02:41,796
because they're used
for programming syntax.

1505
01:02:42,066 --> 01:02:43,456
So for now, realize
what I'm doing.

1506
01:02:44,026 --> 01:02:46,116
I'm declaring a variable
called dollar sign name.

1507
01:02:46,526 --> 01:02:49,676
I am storing and ultimately,
whatever the user types in,

1508
01:02:49,676 --> 01:02:51,866
the value of name and
that's super global,

1509
01:02:51,866 --> 01:02:54,736
but I'm first escaping it
with mysql_real_escape_string.

1510
01:02:55,086 --> 01:02:56,336
Now notice what I'm doing next.

1511
01:02:56,586 --> 01:02:58,706
It turns out POST for captain,

1512
01:02:58,976 --> 01:03:01,196
recall what's submitted
for captain.

1513
01:03:01,296 --> 01:03:02,376
We saw this last week.

1514
01:03:02,636 --> 01:03:06,246
If you checked that box, the
value of ON, O-N is submitted.

1515
01:03:06,246 --> 01:03:08,296
And if you don't check that
box, nothing is submitted.

1516
01:03:08,586 --> 01:03:10,676
So my little trick
here is to just treat

1517
01:03:10,676 --> 01:03:12,216
that kind of as Boolean value.

1518
01:03:12,576 --> 01:03:16,796
If the captain field and the
super global evaluates the true

1519
01:03:16,886 --> 01:03:19,266
and it will if there's
anything there.

1520
01:03:19,266 --> 01:03:22,286
So remember there's a lot of
implicit casting that's possible

1521
01:03:22,286 --> 01:03:26,416
in programing whereby anything
non-zero is essentially true,

1522
01:03:26,416 --> 01:03:28,006
so I'm leveraging
that understanding.

1523
01:03:28,156 --> 01:03:31,776
And I'm saying if the captain
field is anything other

1524
01:03:31,776 --> 01:03:34,996
than false anything other than
blank, then I'm gonna assumed

1525
01:03:34,996 --> 01:03:36,146
that the user check that box

1526
01:03:36,226 --> 01:03:39,086
and I'm gonna set a local
variable called captain equal

1527
01:03:39,086 --> 01:03:39,646
to 1.

1528
01:03:39,996 --> 01:03:42,736
Else, I'm going to say
it captain equal to 0.

1529
01:03:42,916 --> 01:03:45,766
Now here's a curiosity
about PHP too and it kind

1530
01:03:45,826 --> 01:03:47,996
of gets a bad wrap for
being a little too loose

1531
01:03:47,996 --> 01:03:48,946
with some of these details.

1532
01:03:49,286 --> 01:03:52,486
You do not need to
declare variables in PHP.

1533
01:03:52,486 --> 01:03:55,076
Notice, I am just on the
fly whenever the heck I want

1534
01:03:55,076 --> 01:03:57,796
declaring variables, dollar
sign name, dollar sign captain.

1535
01:03:58,016 --> 01:03:59,656
In fact, in the context of C,

1536
01:03:59,656 --> 01:04:01,436
this would be a big
no, no, right?

1537
01:04:01,436 --> 01:04:04,866
This is essentially-- this
variable is scoped here

1538
01:04:04,866 --> 01:04:06,566
and you can use curly
braces in PHP.

1539
01:04:06,656 --> 01:04:09,126
But like C, if you only have one
line of code it doesn't matter.

1540
01:04:09,396 --> 01:04:12,326
In C, I think even on quiz
0, this got us into trouble

1541
01:04:12,546 --> 01:04:14,956
because these variables
were scoped too tightly.

1542
01:04:15,306 --> 01:04:18,806
In PHP, once you declare a
variable you're stock with it.

1543
01:04:18,806 --> 01:04:22,616
It now exists everywhere
in that file even inside

1544
01:04:22,746 --> 01:04:25,366
of curly braces and
outside of them.

1545
01:04:25,716 --> 01:04:27,496
So on the one hand,
this is kind of useful

1546
01:04:27,496 --> 01:04:30,056
because it can let you, the
programmer, be a little more lax

1547
01:04:30,276 --> 01:04:32,136
when it comes to the
structuring of your code

1548
01:04:32,396 --> 01:04:34,766
but it can also very
quickly lead to bad habit.

1549
01:04:34,766 --> 01:04:37,576
So realize here, it feels okay
to be doing what I'm doing

1550
01:04:37,576 --> 01:04:40,856
because I'm always
initializing captain to 1 or 0

1551
01:04:41,116 --> 01:04:43,606
but even I have got corners
in the past where recall

1552
01:04:43,606 --> 01:04:45,226
from a previous example I set

1553
01:04:45,226 --> 01:04:48,956
that variable called dollar
sign error and I set it to true

1554
01:04:49,116 --> 01:04:50,066
but nowhere in my code

1555
01:04:50,066 --> 01:04:51,676
that I ever explicitly
said it's a false.

1556
01:04:51,886 --> 01:04:53,576
I just assumed that
if I don't set it

1557
01:04:53,576 --> 01:04:55,246
to true, it would be false.

1558
01:04:55,246 --> 01:04:57,756
But again this is really just a
different programming paradigm.

1559
01:04:57,866 --> 01:05:00,486
It's a language like
PHP people do tend

1560
01:05:00,486 --> 01:05:02,066
to take these liberties
whereas something

1561
01:05:02,066 --> 01:05:04,836
like C is much more anal about
how you have to write your code.

1562
01:05:05,126 --> 01:05:08,426
So it's a good thing and a
bad thing so long as you start

1563
01:05:08,426 --> 01:05:10,446
to not abuse some
of these features

1564
01:05:10,446 --> 01:05:12,076
by just declaring things
all over the place.

1565
01:05:12,076 --> 01:05:13,936
But here, I proceed
to declare gender.

1566
01:05:14,246 --> 01:05:17,566
I'm storing the value of
the escape version of gender

1567
01:05:17,566 --> 01:05:19,316
in that variable
and same with dorm.

1568
01:05:19,316 --> 01:05:21,106
So in short, with those
several lines of code,

1569
01:05:21,306 --> 01:05:24,166
I just wanted four new
variables, name, captain,

1570
01:05:24,166 --> 01:05:27,136
gender, dorm that stored the
same thing that the user typed

1571
01:05:27,136 --> 01:05:29,336
in but the escape
versions of them.

1572
01:05:29,336 --> 01:05:32,546
Just so I don't accidentally
delete my data by being tricked

1573
01:05:32,816 --> 01:05:36,216
into registering delete
Malan and not David Malan.

1574
01:05:36,426 --> 01:05:38,456
So now I prepared the query.

1575
01:05:38,456 --> 01:05:39,526
There's different
ways to do this.

1576
01:05:39,926 --> 01:05:41,216
But notice what I've done here.

1577
01:05:41,516 --> 01:05:44,186
Ultimately, I need to
execute a query like this.

1578
01:05:44,406 --> 01:05:47,106
INSERT INTO, the
name of the table.

1579
01:05:47,376 --> 01:05:50,476
Then in parenthesis,
I specify the comma--

1580
01:05:50,476 --> 01:05:53,216
a comma separated list
of the fields that I want

1581
01:05:53,216 --> 01:05:54,396
to insert values into.

1582
01:05:54,396 --> 01:05:57,896
What's nice is with the database
table, you can have 20 fields

1583
01:05:58,126 --> 01:06:00,086
and you don't have to
fill all of them out.

1584
01:06:00,086 --> 01:06:02,056
It might be reasonable for
some fields to be blank.

1585
01:06:02,116 --> 01:06:05,386
Maybe someone doesn't have
a website, and so the URL

1586
01:06:05,386 --> 01:06:07,016
of their homepage
should be blank.

1587
01:06:07,016 --> 01:06:08,776
Maybe they don't wanna give
you their email address

1588
01:06:09,046 --> 01:06:10,696
so maybe you don't wanna
fill in that field.

1589
01:06:10,926 --> 01:06:14,036
So with-- by parenthesizing
this list of field names,

1590
01:06:14,036 --> 01:06:17,566
you can say, "I only wanna
insert a row into my table

1591
01:06:18,006 --> 01:06:19,246
for the specific fields."

1592
01:06:19,246 --> 01:06:21,156
In this case, it's of
course all four of them

1593
01:06:21,426 --> 01:06:22,386
but it doesn't have to be.

1594
01:06:22,696 --> 01:06:24,376
Now what values do we
wanna put in there?

1595
01:06:25,016 --> 01:06:27,796
Well notice here, this wrap
onto two lines and that's okay.

1596
01:06:27,796 --> 01:06:32,226
I just move the second down the
below and that's fine in PHP.

1597
01:06:32,226 --> 01:06:36,046
Notice I have now values,
parenthesis, close parenthesis,

1598
01:06:36,046 --> 01:06:39,006
and then another comma separated
list but you have to bear

1599
01:06:39,006 --> 01:06:41,066
in mind and this is one of the
most common sort of gotchas

1600
01:06:41,126 --> 01:06:42,646
in office hours and
in these psets,

1601
01:06:43,036 --> 01:06:45,346
you realize that
anytime you have a string

1602
01:06:45,346 --> 01:06:47,226
in PHP, you must quote it.

1603
01:06:47,356 --> 01:06:49,666
Now you can use double quotes,
you can use single quotes

1604
01:06:49,666 --> 01:06:50,736
so long as you're consistent.

1605
01:06:50,966 --> 01:06:53,816
I use single quotes here but
notice I put single quotes

1606
01:06:53,816 --> 01:06:56,826
around name, around gender,
and around dorm but not

1607
01:06:56,826 --> 01:06:59,976
around captain because captain
I decided would be an integer

1608
01:07:00,086 --> 01:07:01,656
so it doesn't need
to have them there.

1609
01:07:01,996 --> 01:07:04,746
So at the end of the day, the
string that I've just stored

1610
01:07:04,806 --> 01:07:08,456
in a variable called SQL looks
a little something like this.

1611
01:07:08,716 --> 01:07:18,316
Insert into registrants the
name, captain, gender, dorm,

1612
01:07:18,886 --> 01:07:24,446
values, "David Malan"
captain I think I said--

1613
01:07:24,706 --> 01:07:29,276
well, I think I sent an M
and then dorm was Mathews.

1614
01:07:29,476 --> 01:07:32,816
So this is the string that I've
just constructed dynamically

1615
01:07:33,096 --> 01:07:37,156
by way of using these
variables and these placeholder,

1616
01:07:37,156 --> 01:07:38,996
these variables inside
of this bigger string.

1617
01:07:39,216 --> 01:07:41,286
So the magic then happens
with this one line of code.

1618
01:07:41,466 --> 01:07:44,256
I've now constructed what's
called a SQL statement,

1619
01:07:44,256 --> 01:07:46,456
a SQL query, that's
the insert statement.

1620
01:07:46,756 --> 01:07:50,436
I then past it to the function
called my SQL query whose

1621
01:07:50,436 --> 01:07:52,356
purpose in life because
I've already connected

1622
01:07:52,356 --> 01:07:54,346
to the database, I've
already selected my database,

1623
01:07:54,346 --> 01:07:57,436
all that happened before is
now to execute that query

1624
01:07:57,436 --> 01:08:01,016
against the database and so
the reason that this row ended

1625
01:08:01,016 --> 01:08:02,876
up in my table a moment ago was

1626
01:08:02,906 --> 01:08:05,696
because that insert
statement just got executed.

1627
01:08:05,946 --> 01:08:07,786
In fact, I can simulate
this myself.

1628
01:08:07,916 --> 01:08:10,816
Rather than go through the
web, let me actually show you

1629
01:08:10,816 --> 01:08:13,046
that this thing is in
fact doing what I say.

1630
01:08:13,276 --> 01:08:16,216
I'm gonna go to PHP my
admin, just this little tool.

1631
01:08:16,216 --> 01:08:17,476
We've seen the structure tab.

1632
01:08:17,566 --> 01:08:19,466
That just reminds me what
this thing looks like.

1633
01:08:19,706 --> 01:08:20,736
We've seen the browse tab.

1634
01:08:20,736 --> 01:08:22,086
That shows me what's
inside there.

1635
01:08:22,366 --> 01:08:24,556
I can actually interact
with SQL directly.

1636
01:08:24,556 --> 01:08:28,606
If I click the SQL tab, notice
I just get a big text area

1637
01:08:28,906 --> 01:08:31,356
that I can type any commands
into that I want and here too,

1638
01:08:31,356 --> 01:08:33,216
this is why it's a
wonderfully useful learning tool

1639
01:08:33,456 --> 01:08:35,956
because you can just play and it
doesn't really matter especially

1640
01:08:35,986 --> 01:08:38,586
when you have no data to lose,
if you get something wrong.

1641
01:08:38,816 --> 01:08:41,236
So I'm gonna try pasting
this in and instead

1642
01:08:41,236 --> 01:08:42,346
of registering myself,

1643
01:08:42,586 --> 01:08:45,006
I'll register Jan Sue
[phonetic] this time.

1644
01:08:45,006 --> 01:08:48,346
I'll change this to
female, this to Eliot

1645
01:08:48,346 --> 01:08:53,716
and then let me go back here and
click go and now it says up top,

1646
01:08:53,716 --> 01:08:56,496
one row inserted, so
let's see if that's true.

1647
01:08:56,496 --> 01:08:59,116
Click Browse, Zoom
Out and sure enough,

1648
01:08:59,206 --> 01:09:00,886
now I have two rows
in this table.

1649
01:09:01,106 --> 01:09:02,866
Now, suppose, I want to
get all those users back,

1650
01:09:03,456 --> 01:09:04,766
come to the question
just for a moment.

1651
01:09:05,046 --> 01:09:07,066
Now I want them all back,
I'm gonna actually go

1652
01:09:07,066 --> 01:09:11,096
to another piece of code I wrote
here called registrants dot PHP

1653
01:09:11,096 --> 01:09:14,086
and now I dynamically
generated a webpage

1654
01:09:14,086 --> 01:09:16,966
that executed instantaneously
that does not have David

1655
01:09:16,966 --> 01:09:19,346
or Jan Sue hard coded into
it but it's apparently

1656
01:09:19,346 --> 01:09:22,286
out putting a bulleted list
by way of a select query

1657
01:09:22,386 --> 01:09:23,386
which we'll see in
just a second.

1658
01:09:23,596 --> 01:09:23,686
Yeah.

1659
01:09:24,516 --> 01:09:33,776
[ Inaudible Remark ]

1660
01:09:34,276 --> 01:09:36,516
>> Very similar, yes.

1661
01:09:36,696 --> 01:09:38,566
So in C, you can use sprintf.

1662
01:09:38,566 --> 01:09:40,706
That actually exists
in PHP as well.

1663
01:09:40,926 --> 01:09:43,396
There is many, many ways to
construct the string on the fly

1664
01:09:43,646 --> 01:09:45,906
in PHP and just plugging
in these variables

1665
01:09:45,906 --> 01:09:49,356
as I've done here is
legitimate in PHP and frankly,

1666
01:09:49,586 --> 01:09:51,236
it's arguably a little simpler

1667
01:09:51,236 --> 01:09:54,466
than having use those percent
S placeholders everywhere.

1668
01:09:55,336 --> 01:09:57,106
So let me draw our
attention then to this.

1669
01:09:57,506 --> 01:10:00,496
So this might be for instance
the PHP page that I give

1670
01:10:00,536 --> 01:10:02,796
to the proctor when it
comes time for him or her

1671
01:10:02,796 --> 01:10:05,456
to see who's registered
for some Spork at the top

1672
01:10:05,456 --> 01:10:07,536
of this page, registrants
dot PHP.

1673
01:10:07,706 --> 01:10:09,596
Notice that I connect
to the database again

1674
01:10:09,596 --> 01:10:11,036
with my username,
with my password.

1675
01:10:11,216 --> 01:10:14,106
I select the same database
and then I create this query,

1676
01:10:14,416 --> 01:10:16,956
select star where
star means everything,

1677
01:10:16,956 --> 01:10:19,216
give me all of the
rows from registrants.

1678
01:10:19,506 --> 01:10:22,616
Now I execute this query but
this time because I'm asking

1679
01:10:22,616 --> 01:10:25,126
for data, I have to
remember the return value.

1680
01:10:25,126 --> 01:10:27,816
I can't just call my SQL
query and then call it a day.

1681
01:10:28,016 --> 01:10:30,556
I need to get back the
server's answer so I store

1682
01:10:30,556 --> 01:10:32,116
in a variable a called result.

1683
01:10:32,396 --> 01:10:33,746
Now, let's fast forward.

1684
01:10:33,786 --> 01:10:37,966
I seem to be exiting PHP mode
outputting a default webpage

1685
01:10:38,246 --> 01:10:41,726
but then notice this, what's
really neat, I have this UL tag

1686
01:10:41,726 --> 01:10:44,426
which stands for Unordered
List and if you look this

1687
01:10:44,426 --> 01:10:48,516
up in the manual, a UL tag has
to have LI, list item tags,

1688
01:10:48,586 --> 01:10:49,976
inside of it and every one

1689
01:10:49,976 --> 01:10:51,976
of those list item
tags becomes a bullet.

1690
01:10:52,206 --> 01:10:54,936
And so what I'm doing here is
outputting one or more bullets

1691
01:10:55,316 --> 01:10:57,926
so how am I iterating over
the results and here is

1692
01:10:57,926 --> 01:11:00,266
where the really neat
feature is of this prog--

1693
01:11:00,266 --> 01:11:02,286
of this being able to
program against the database.

1694
01:11:02,676 --> 01:11:06,096
I can call a function
called my SQL fetch array.

1695
01:11:06,526 --> 01:11:08,046
Where do I want to
fetch an array from?

1696
01:11:08,276 --> 01:11:10,726
I specified dollars on
results as the argument

1697
01:11:10,726 --> 01:11:13,426
and that says fetch them from
the results I've just got

1698
01:11:13,426 --> 01:11:16,446
from the database on every
iteration of this loop,

1699
01:11:16,576 --> 01:11:21,036
store that array in a
variable called dollar sign row

1700
01:11:21,036 --> 01:11:23,096
because conceptually,
when I say select star,

1701
01:11:23,096 --> 01:11:24,526
that means give me all the rows.

1702
01:11:24,776 --> 01:11:27,626
So when I iterate over each
of these, I'm being handed

1703
01:11:27,626 --> 01:11:30,696
that row really nicely
as an associative array.

1704
01:11:30,956 --> 01:11:34,576
So just these columns have
names, name and dorm and gender

1705
01:11:34,576 --> 01:11:38,486
and captain, I can now
get those values just

1706
01:11:38,486 --> 01:11:40,126
as though they were
from an HTML form.

1707
01:11:40,126 --> 01:11:42,796
This time they're coming from a
database by way of their names

1708
01:11:43,026 --> 01:11:45,946
and so this time, I'm gonna
print a list item tag then I'm

1709
01:11:45,946 --> 01:11:48,896
gonna close it but inside
of that, I'm gonna print

1710
01:11:48,896 --> 01:11:52,086
out dollar sign row "name"

1711
01:11:52,526 --> 01:11:55,256
and what that's gonna do is I'll
put David Malan then Jan Sue

1712
01:11:55,256 --> 01:11:57,696
[inaudible] and then
that's it for that loop.

1713
01:11:57,936 --> 01:12:01,246
And as an aside too to get us
in the habit of best practices,

1714
01:12:01,246 --> 01:12:04,076
HTML special charge is a
function that also takes care

1715
01:12:04,076 --> 01:12:05,726
of any dangerous
characters so that

1716
01:12:05,726 --> 01:12:07,816
if a malicious user
actually typed in something

1717
01:12:07,816 --> 01:12:11,616
like open bracket blink close
bracket, they couldn't trick me

1718
01:12:11,826 --> 01:12:14,396
into outputting a webpage
for this proctor where all

1719
01:12:14,396 --> 01:12:17,316
of the names are actually
blinking by having entered,

1720
01:12:17,316 --> 01:12:19,526
again, a blink tag and
not an actual name.

1721
01:12:19,526 --> 01:12:21,036
So we're really just
scratching the surface

1722
01:12:21,036 --> 01:12:21,976
of all of these features.

1723
01:12:22,176 --> 01:12:24,506
On Wednesday, we'll introduce
a language called Ajax--

1724
01:12:24,506 --> 01:12:27,016
JavaScript and with that
a technology called Ajax

1725
01:12:27,016 --> 01:12:29,716
with which all of today's
modern sites are now leveraging.

1726
01:12:29,816 --> 01:12:34,156
We'll see you then.

1727
01:12:34,656 --> 01:12:37,540
[ Inaudible Remark ]