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>> JASON HIRSCHHORN: Welcome.

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So just a few announcements
before we start.

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So sections, everyone should
have sectioned already.

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Sections normally run
from Sunday to Tuesday.

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So you guys should get your assignments.

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And then I think next week
you'll be with your actual TFs.

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So if you have any questions, or
trouble, or you forgot to section.

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Some people do that.

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Just let us know.

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Shoot us an email at heads.

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>> Then office hours.

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We started office hours last week.

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Office hours every week.

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Monday is in Leverett 8:00 to 11:00.

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Tuesdays in the quad,
so Cabot 8:00 to 11:00.

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Wednesday, Mather 8:30 to 11:30.

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And Thursday Annenberg 8:00 to 11:00.

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>> So Scratch, a lot of people
don't need office hours

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help for Scratch, which
is completely fine.

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If you do, that's
absolutely fine as well.

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But in the future, the problem
sets, they get much harder.

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So this is going to be your friend.

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Definitely go to office hours.

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Plan on going to office hours.

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When you get to problem
set four, five, six, seven,

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you need to go to office hours.

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That's where a lot the help
and the work gets done.

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>> I think last year, just for
example, on Thursday night--

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so I think the problem
sets were due on Friday.

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So Thursday night, we would have
200, 250 students at office hours.

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So definitely make use of these.

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These are your best friends.

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Like this is where if you're
stuck on a problem set,

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this is where you'll probably get help.

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So office hours.

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OK so those are announcements.

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Announcements are done, so let's start.

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>> OK, the appliance.

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Did everybody download
the appliance yet?

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No.

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As in so so.

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I kind of downloaded the appliance.

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Right so the appliance is new
this year, so we're probably

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going to have some bugs in it.

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So please download it
as early as possible.

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So problem set one is going to tell
you exactly how to download it.

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Getting started installing right here.

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It's going to tell you how
to download the appliance.

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>> So definitely download the
appliance sooner rather than later.

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Instructions are in the P set spec.

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So if you wait until Wednesday
night, and then you have trouble,

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and you send us an email at
midnight on Wednesday night

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that you can't download
the appliance, that's

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not a legit reason for an extension.

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You need to do it now,
and you will have trouble.

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I tried to download it last night.

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I ran into a little bit of trouble.

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If you do run into trouble
installing, definitely

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hit retry, because I just hit retry a
couple times, and eventually it worked,

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which doesn't make any
sense, but it does.

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So definitely retry, but if you
come up against a brick wall,

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shoot us an email at heads, and we'll
be more than happy to help you guys.

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What's up?

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>> STUDENT: Just a quick question.

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If they check style, there's a part
that says we didn't include this.

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JASON HIRSCHHORN: Not yet.

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STUDENT: It says execute it.

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How do you execute that to
make sure it's in your system?

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>> JASON HIRSCHHORN: You're
going to run a bash command.

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I'll go over that later.

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Cool.

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So the appliance can be a
little bit intimidating,

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because you're used to kind of
running in graphical user interface.

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So Scratch was a graphical user
interface, so what do I mean by that?

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What I mean is that
when you're programming,

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you're basically using blocks of code.

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You can see the code
and stuff like that.

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>> The appliance, you're going to be doing
things in a command line environment.

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And so for the rest of
your programming lives,

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you're going to be doing things
in the command line environment.

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So it's good to jump in early
and get some experience.

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So let's do it.

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So that's Rob.

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>> OK, so let's just jump
into command line stuff.

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So this is the appliance.

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Can anybody tell me why
we use an appliance?

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What is the appliance?

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Does anybody know?

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What's up?

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>> STUDENT: It's just a virtual machine
that you run your machine so that you

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can get over the OS
disagreements between Mac and PC.

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JASON HIRSCHHORN: Perfect.

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STUDENT: It's a universal template.

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JASON HIRSCHHORN: Yeah, it's
like a universal template.

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That's perfect.

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So yeah, it's a virtual machine.

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So it's basically an operating system.

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This is an operating system.

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This is equivalent to your
Mac, or you PC, or your Linux.

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This is the exact same.

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And so you can do similar stuff.

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If you wanted to, you could
go online for example.

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You can't really see it, but
right here, Google Chrome.

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You can go online if you want to.

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This is an operating system.

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And the reason we do that is because
it's much easier when we're handing out

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instructions and everything.

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If it's just a uniform environment,
it's much easier for us,

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and it's much easier for you.

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You're not going to run into
it run into any idiosyncrasies

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when you're programming.

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We know exactly what
you're going to run into.

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So the appliance is here.

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>> So when you're starting
programming, you're

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going to go down to
the left hand corner.

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There's a little box.

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You're going to click it.

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This is your terminal window.

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So this is where you're going
to be a lot of the semester.

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So let me zoom in a little bit.

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>> OK, so getting around a terminal
window is a little bit different.

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First, there's no icons.

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I can't click anything.

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There's nothing to click.

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So you have to figure out a way to
figure out where you are, what's here,

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and how to move around.

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>> So the two most useful commands probably
are ls-- so what do you think ls does?

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>> STUDENT: List.

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JASON HIRSCHHORN: Lists, yeah.

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It just lists algorithms
within the directory.

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And then cd.

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So let's say I wanted to
cd CS50, what did that do?

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Yeah?

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>> STUDENT: Changes your directory.

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JASON HIRSCHHORN: Perfect, yeah.

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It just changes the directory.

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So let's go back.

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So how do I go back?

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So let's say I wanted to go
back to the previous directory.

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Yeah sure.

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>> STUDENT: I think you write
cd just without anything.

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JASON HIRSCHHORN: You can do that.

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So perfect.

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So if I write cd, this is
actually going to pop me

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back up to the home directory.

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So you see this tilde,
that's going to pop me

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way back up to where the tilde is.

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So it's going to pop me up
back to the home directory.

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But let's say I did something like this.

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Let's say cd CS50.

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ls again.

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I've got other stuff. cd super section.

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cd file, so I'm going deep.

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And then let's say I want to
just pop back up to the top.

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cd.

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Let's say I don't want to do that.

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Let's say I just want to pop back up to
the directory that was right above me.

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How do I do that?

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So let's say cd CS50.

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cd supersection.

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So let's I'm here.

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Let's say I just want
to pop up one time.

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How do I do that?

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Yeah, what's up?

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>> STUDENT: You just type
cd supersection again.

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>> JASON HIRSCHHORN: You could do that.

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Well I'm in supersection.

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>> STUDENT: Oh, the one before.

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>> JASON HIRSCHHORN: Yeah,
so you could do that.

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You do cd ~CS50.

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So if you look here, this
is your path right here.

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That's your path.

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So you could seriously
just go cd ~/CS50.

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Boom, you're there.

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What's an easier way to do it though?

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That was perfectly correct, but
what's a slightly easier way

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to do it, because a lot
of times you're going

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to be jumping in directories,
jumping out of directories.

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So let's go back.

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cd supersection.

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So let's say I want to
get back real quick.

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You can do something like cd dot dot.

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That's going to pop
you back up real quick.

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So cd supersection.

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cd files.

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Let's say I'm here.

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By the way, clear is good, because my
window was getting a little bit messy.

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So ls, so I don't want to
be here anymore. cd dot dot.

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Take me one up.

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Cd dot dot takes me one up.

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Cd dot dot and back to my home.

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>> OK, so cd, ls.

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Probably the most important
things, because you're

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going to need to know where you are.

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ls is going to tell you
where you are, and cd

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is how you're going to jump around.

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>> You can also do some other cool stuff.

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So for example ls.

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ls is just going to show you
the directories in your file.

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It's also going to show you the files.

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But it's just going to
show you what's there.

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>> If you wanted something
a little bit more cool,

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and you're going to actually do
this in a couple weeks. ls dash l.

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That prints out a
little more information.

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Can anybody guess on the left hand
side the drwx, rwx and stuff like that.

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Does anybody have an idea
what that might mean?

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>> STUDENT: Permissions.

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>> JASON HIRSCHHORN: Yeah, perfect.

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Permissions.

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So you're going to
have to deal with this

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when you do web programming later on.

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If you've ever gone online,
and you've clicked on an image

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or clicked on a field,
and it said permission--

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like permission not allowed, or like
permission not granted or whatever,

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that's because when
they're programming, they

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haven't set these permissions
to let you do that.

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So where that comes from.

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>> OK, so that's cool.

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So we jumped around.

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We can look at stuff in our directory.

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But how do we make stuff?

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I've got directories here.

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That's awesome.

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How do I make a new directory?

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Say I want to make a new
directory for right now.

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You can do something like this, mkdir.

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So make directory.

264
00:09:17,244 --> 00:09:19,035
So what do you want to
call this directory?

265
00:09:19,035 --> 00:09:21,454

266
00:09:21,454 --> 00:09:22,162
STUDENT: Awesome.

267
00:09:22,162 --> 00:09:24,107

268
00:09:24,107 --> 00:09:25,190
JASON HIRSCHHORN: Awesome.

269
00:09:25,190 --> 00:09:25,690
I love it.

270
00:09:25,690 --> 00:09:26,650

271
00:09:26,650 --> 00:09:27,790
Make directory awesome.

272
00:09:27,790 --> 00:09:28,802

273
00:09:28,802 --> 00:09:29,510
And there you go.

274
00:09:29,510 --> 00:09:30,809
So we need a list.

275
00:09:30,809 --> 00:09:31,850
You have a new directory.

276
00:09:31,850 --> 00:09:33,180
And you can tell it's a
directory in your appliance

277
00:09:33,180 --> 00:09:34,850
because it's got this color, right?

278
00:09:34,850 --> 00:09:37,970
So it's like a bluish
purple or whatever.

279
00:09:37,970 --> 00:09:39,260

280
00:09:39,260 --> 00:09:40,020
So let's change.

281
00:09:40,020 --> 00:09:40,860
Let's change directory.

282
00:09:40,860 --> 00:09:42,609
Let's go into directory--
yeah, what's up?

283
00:09:42,609 --> 00:09:46,114
STUDENT: Is there a list of
all these [INAUDIBLE] online?

284
00:09:46,114 --> 00:09:48,780
JASON HIRSCHHORN: Yeah, I'll put
them up on-- we'll have slides.

285
00:09:48,780 --> 00:09:49,407
It'll be a PDF.

286
00:09:49,407 --> 00:09:50,740
We'll put them up for everybody.

287
00:09:50,740 --> 00:09:53,170
Yeah, sorry it's a lot of commands.

288
00:09:53,170 --> 00:09:56,092
if you want me to slow down, or
go back, or anything like that,

289
00:09:56,092 --> 00:09:57,050
definitely let me know.

290
00:09:57,050 --> 00:09:59,510
It's a lot to absorb right away.

291
00:09:59,510 --> 00:10:00,059
What's up?

292
00:10:00,059 --> 00:10:02,100
STUDENT: Can I ask a
potentially stupid question?

293
00:10:02,100 --> 00:10:03,240
JASON HIRSCHHORN: There's
no stupid questions.

294
00:10:03,240 --> 00:10:04,031
STUDENT: There are.

295
00:10:04,031 --> 00:10:06,462

296
00:10:06,462 --> 00:10:09,384
A directory is for just looking
at information where you store it.

297
00:10:09,384 --> 00:10:09,871
>> JASON HIRSCHHORN: Yeah.

298
00:10:09,871 --> 00:10:11,829
>> STUDENT: Is that essentially
what you're doing?

299
00:10:11,829 --> 00:10:14,741
So when we make something,
hello world or whatever,

300
00:10:14,741 --> 00:10:16,202
it's stored in the directory, yes?

301
00:10:16,202 --> 00:10:16,689
>> JASON HIRSCHHORN: Yeah.

302
00:10:16,689 --> 00:10:18,637
>> STUDENT: Is that true for everything.

303
00:10:18,637 --> 00:10:20,340
Everything is stored in the directory.

304
00:10:20,340 --> 00:10:20,680
>> JASON HIRSCHHORN: Yeah.

305
00:10:20,680 --> 00:10:22,490
Whenever you make it,
whatever directory you're in,

306
00:10:22,490 --> 00:10:24,615
it's going to basically
store it in that directory.

307
00:10:24,615 --> 00:10:27,680
STUDENT: And when we're calling it,
we're calling it from the directory.

308
00:10:27,680 --> 00:10:30,013
>> JASON HIRSCHHORN: Yeah, so
the directory is where it es.

309
00:10:30,013 --> 00:10:32,910
So it's kind of like if you have
a new folder on your desktop

310
00:10:32,910 --> 00:10:36,530
and then you write a text
file, put it in that folder,

311
00:10:36,530 --> 00:10:38,160
that file is in that folder.

312
00:10:38,160 --> 00:10:39,690
Does that make sense?

313
00:10:39,690 --> 00:10:40,570
>> STUDENT: Yeah.

314
00:10:40,570 --> 00:10:41,646
>> JASON HIRSCHHORN: Yeah, what's up?

315
00:10:41,646 --> 00:10:43,390
>> STUDENT: Can I just ask you to
make it a little bit bigger?

316
00:10:43,390 --> 00:10:43,940
>> JASON HIRSCHHORN: Oh, yeah.

317
00:10:43,940 --> 00:10:44,439
Sorry.

318
00:10:44,439 --> 00:10:45,730

319
00:10:45,730 --> 00:10:46,732
The projector is so bad.

320
00:10:46,732 --> 00:10:48,440
We had so much trouble
with this earlier.

321
00:10:48,440 --> 00:10:52,240

322
00:10:52,240 --> 00:10:53,872
Is that better?

323
00:10:53,872 --> 00:10:55,617
Is that too big?

324
00:10:55,617 --> 00:10:57,080
>> STUDENT: No, no it's not.

325
00:10:57,080 --> 00:10:58,440
>> JASON HIRSCHHORN: No, it's not.

326
00:10:58,440 --> 00:10:59,170
Is it too small?

327
00:10:59,170 --> 00:11:00,480

328
00:11:00,480 --> 00:11:01,030
What's up?

329
00:11:01,030 --> 00:11:03,760
>> STUDENT: I'm sorry, what's
the command for clearing?

330
00:11:03,760 --> 00:11:04,926
>> JASON HIRSCHHORN: Oh, clear.

331
00:11:04,926 --> 00:11:07,085

332
00:11:07,085 --> 00:11:10,230
If you want to clear, just
type clear. clear enter.

333
00:11:10,230 --> 00:11:12,104

334
00:11:12,104 --> 00:11:14,020
On the last appliance,
what it basically does,

335
00:11:14,020 --> 00:11:17,060
it doesn't clear your information,
it just kind of shift everything

336
00:11:17,060 --> 00:11:18,350
down one screen.

337
00:11:18,350 --> 00:11:21,200
So if you typed clear-- for
example let's say I'm scrolling up.

338
00:11:21,200 --> 00:11:21,900
I can scroll up.

339
00:11:21,900 --> 00:11:22,941
This is everything I did.

340
00:11:22,941 --> 00:11:23,750

341
00:11:23,750 --> 00:11:29,500
But if I type clear, and then
I scroll up, here's my stuff.

342
00:11:29,500 --> 00:11:32,600
So it's not erasing it, it's just
basically giving you a new frame.

343
00:11:32,600 --> 00:11:33,983

344
00:11:33,983 --> 00:11:35,940
>> STUDENT: How do you
[INAUDIBLE] a directory?

345
00:11:35,940 --> 00:11:37,428
>> JASON HIRSCHHORN: We'll get there.

346
00:11:37,428 --> 00:11:39,536
>> [LAUGHTER]

347
00:11:39,536 --> 00:11:40,160
Slow your roll.

348
00:11:40,160 --> 00:11:41,720

349
00:11:41,720 --> 00:11:42,370
All right.

350
00:11:42,370 --> 00:11:45,590
OK, so so we're in a
directory right now.

351
00:11:45,590 --> 00:11:48,360

352
00:11:48,360 --> 00:11:52,700
So David, I think in lecture
he did some cool stuff.

353
00:11:52,700 --> 00:11:53,875
So let's write a program.

354
00:11:53,875 --> 00:11:56,000

355
00:11:56,000 --> 00:11:58,540
So you can do that a
number of different ways.

356
00:11:58,540 --> 00:12:00,040
You can use any kind of text editor.

357
00:12:00,040 --> 00:12:03,090
You can use Nano, you
can use Vim, Emacs.

358
00:12:03,090 --> 00:12:05,110
Those are slightly more complicated.

359
00:12:05,110 --> 00:12:06,822

360
00:12:06,822 --> 00:12:09,030
Or you can use something in
here that's called gedit.

361
00:12:09,030 --> 00:12:12,716

362
00:12:12,716 --> 00:12:13,215
Sorry.

363
00:12:13,215 --> 00:12:18,590

364
00:12:18,590 --> 00:12:19,480
gedit is not happy.

365
00:12:19,480 --> 00:12:21,870

366
00:12:21,870 --> 00:12:27,870
So gedit is basically
just a text editor.

367
00:12:27,870 --> 00:12:30,780
Just like I text edit word
processor or something like that.

368
00:12:30,780 --> 00:12:33,260
So it's got a nice
interface just like this.

369
00:12:33,260 --> 00:12:36,340
So you do something like that.

370
00:12:36,340 --> 00:12:39,190
So actually let me give it
name because I never did that.

371
00:12:39,190 --> 00:12:40,620

372
00:12:40,620 --> 00:12:43,170
>> So what do you want to
name our first program?

373
00:12:43,170 --> 00:12:44,566
It's just going to say hi.

374
00:12:44,566 --> 00:12:45,441
>> STUDENT: [INAUDIBLE].

375
00:12:45,441 --> 00:12:46,470

376
00:12:46,470 --> 00:12:48,180
>> JASON HIRSCHHORN: You lack imagination.

377
00:12:48,180 --> 00:12:49,615
OK, gedit.

378
00:12:49,615 --> 00:12:50,115
Hi.

379
00:12:50,115 --> 00:12:51,166

380
00:12:51,166 --> 00:12:52,040
I'm going to do .txt.

381
00:12:52,040 --> 00:12:54,470

382
00:12:54,470 --> 00:12:55,680
OK, so here it is.

383
00:12:55,680 --> 00:12:57,820
So let's write a program.

384
00:12:57,820 --> 00:13:01,280
So I think you saw this in lecture.

385
00:13:01,280 --> 00:13:02,380
You need a main function.

386
00:13:02,380 --> 00:13:04,690

387
00:13:04,690 --> 00:13:05,190
Boop.

388
00:13:05,190 --> 00:13:06,910

389
00:13:06,910 --> 00:13:08,280
So this is just a main function.

390
00:13:08,280 --> 00:13:10,550

391
00:13:10,550 --> 00:13:11,050
Bigger?

392
00:13:11,050 --> 00:13:11,550
Yeah, sorry.

393
00:13:11,550 --> 00:13:16,690

394
00:13:16,690 --> 00:13:19,102
OK so you need a main function.

395
00:13:19,102 --> 00:13:20,810
I think I'm jumping
the gun a little bit,

396
00:13:20,810 --> 00:13:23,750
but it's never bad to get
used to this kind of stuff.

397
00:13:23,750 --> 00:13:25,680
>> So a main function,
every C program you're

398
00:13:25,680 --> 00:13:28,555
going to write for the rest of this
course will have a main function.

399
00:13:28,555 --> 00:13:29,004

400
00:13:29,004 --> 00:13:29,920
Does anybody know why?

401
00:13:29,920 --> 00:13:31,231

402
00:13:31,231 --> 00:13:32,105
What's up?

403
00:13:32,105 --> 00:13:32,980
>> STUDENT: Start.

404
00:13:32,980 --> 00:13:35,020
>> JASON HIRSCHHORN: Exactly, so it
tells your program where to start.

405
00:13:35,020 --> 00:13:38,169
So if you don't have a main function,
and you compile this and stuff,

406
00:13:38,169 --> 00:13:39,710
it's not going to know were to start.

407
00:13:39,710 --> 00:13:41,810
Main is always where it starts.

408
00:13:41,810 --> 00:13:46,910
So you have a main function, and then
does anybody remember how to print?

409
00:13:46,910 --> 00:13:47,699
>> STUDENT: printf.

410
00:13:47,699 --> 00:13:48,990
JASON HIRSCHHORN: Yeah, printf.

411
00:13:48,990 --> 00:13:50,280

412
00:13:50,280 --> 00:13:52,794
printf hi.

413
00:13:52,794 --> 00:13:55,080

414
00:13:55,080 --> 00:14:02,450
OK, now I have set you guys up
to fail, but will this compile.

415
00:14:02,450 --> 00:14:03,290
>> STUDENT: No.

416
00:14:03,290 --> 00:14:03,520
>> JASON HIRSCHHORN: Why?

417
00:14:03,520 --> 00:14:04,830
There's multiple reasons why.

418
00:14:04,830 --> 00:14:06,460

419
00:14:06,460 --> 00:14:07,300
Sure.

420
00:14:07,300 --> 00:14:09,700
>> STUDENT: It doesn't have
the standard [INAUDIBLE].

421
00:14:09,700 --> 00:14:10,783
>> JASON HIRSCHHORN: Perfect.

422
00:14:10,783 --> 00:14:12,122
So what's this called up here?

423
00:14:12,122 --> 00:14:13,540
>> STUDENT: [INAUDIBLE]

424
00:14:13,540 --> 00:14:14,540
>> JASON HIRSCHHORN: It's
a header file, right?

425
00:14:14,540 --> 00:14:15,331
It's a header file.

426
00:14:15,331 --> 00:14:16,460
And you're exactly right.

427
00:14:16,460 --> 00:14:17,376
Both of you are right.

428
00:14:17,376 --> 00:14:21,340
So to include that, I just do pound
include standard input output .h.

429
00:14:21,340 --> 00:14:22,787

430
00:14:22,787 --> 00:14:23,620
Am I good to go now?

431
00:14:23,620 --> 00:14:27,570

432
00:14:27,570 --> 00:14:28,520
Would this compile?

433
00:14:28,520 --> 00:14:29,263
>> STUDENT: No.

434
00:14:29,263 --> 00:14:30,346
JASON HIRSCHHORN: Why not?

435
00:14:30,346 --> 00:14:32,417
STUDENT: It's a [INAUDIBLE] text.

436
00:14:32,417 --> 00:14:33,750
JASON HIRSCHHORN: Yeah, awesome.

437
00:14:33,750 --> 00:14:34,900

438
00:14:34,900 --> 00:14:36,420
So I just made it.

439
00:14:36,420 --> 00:14:46,130
So I saved it, but gedit hi.txt.

440
00:14:46,130 --> 00:14:47,170

441
00:14:47,170 --> 00:14:50,080
So now if I do ls, here it is.

442
00:14:50,080 --> 00:14:50,580
Right here.

443
00:14:50,580 --> 00:14:51,716
Oh, it's not in awesome.

444
00:14:51,716 --> 00:14:52,590
I must have gone out.

445
00:14:52,590 --> 00:14:53,740

446
00:14:53,740 --> 00:14:54,620
Oh, perfect.

447
00:14:54,620 --> 00:14:56,200
How do we put this in awesome?

448
00:14:56,200 --> 00:14:59,150
So I don't want it here in my home
directory with everything else.

449
00:14:59,150 --> 00:15:00,832
I want to put it in the folder.

450
00:15:00,832 --> 00:15:01,540
How do I do that?

451
00:15:01,540 --> 00:15:09,530

452
00:15:09,530 --> 00:15:10,210
>> Not too hard.

453
00:15:10,210 --> 00:15:13,566

454
00:15:13,566 --> 00:15:14,065
Move.

455
00:15:14,065 --> 00:15:16,410

456
00:15:16,410 --> 00:15:18,700
So we've already learned ls, list.

457
00:15:18,700 --> 00:15:19,900
cd to change directories.

458
00:15:19,900 --> 00:15:21,739
cd dot dot to bump out of directories.

459
00:15:21,739 --> 00:15:23,780
And now we're going to
start moving around files.

460
00:15:23,780 --> 00:15:30,210
So to move just move hi.txt, and
I'm going to put it in awesome.

461
00:15:30,210 --> 00:15:31,270

462
00:15:31,270 --> 00:15:32,310
>> Just be careful.

463
00:15:32,310 --> 00:15:34,976
Whenever you're writing in the
command line, everything matters.

464
00:15:34,976 --> 00:15:37,020
So uppercase matters.

465
00:15:37,020 --> 00:15:40,440
If I had done lowercase a, it's
not going to know what's going on.

466
00:15:40,440 --> 00:15:42,840
So everything matters
to be very specific.

467
00:15:42,840 --> 00:15:45,120
>> So run that ls.

468
00:15:45,120 --> 00:15:46,310
It's no longer here.

469
00:15:46,310 --> 00:15:48,040
Let's change directory into awesome.

470
00:15:48,040 --> 00:15:49,380

471
00:15:49,380 --> 00:15:49,880
ls.

472
00:15:49,880 --> 00:15:50,782

473
00:15:50,782 --> 00:15:51,490
Boom, it's there.

474
00:15:51,490 --> 00:15:53,940
And somebody mentioned why
this would not compile.

475
00:15:53,940 --> 00:15:55,410
Why is not going to compile again?

476
00:15:55,410 --> 00:15:56,891

477
00:15:56,891 --> 00:15:57,390
Yeah?

478
00:15:57,390 --> 00:15:58,690
>> STUDENT: It's not in a .c.

479
00:15:58,690 --> 00:15:59,060
>> JASON HIRSCHHORN: Perfect.

480
00:15:59,060 --> 00:16:01,686
It's not a .c, s so how am I
going to rename it to a .c?

481
00:16:01,686 --> 00:16:03,120
What's an easy way to do it?

482
00:16:03,120 --> 00:16:05,200

483
00:16:05,200 --> 00:16:06,720
Let's use the command we just did.

484
00:16:06,720 --> 00:16:13,860
So we're just going to
move hi.txt to hi.c.

485
00:16:13,860 --> 00:16:15,160

486
00:16:15,160 --> 00:16:16,710
ls hi.c.

487
00:16:16,710 --> 00:16:19,990
And then just for fun, let's
just jump into this real quick.

488
00:16:19,990 --> 00:16:24,291

489
00:16:24,291 --> 00:16:24,790
hi.c.

490
00:16:24,790 --> 00:16:26,290

491
00:16:26,290 --> 00:16:28,400
You'll notice it's nice and colorful.

492
00:16:28,400 --> 00:16:30,490

493
00:16:30,490 --> 00:16:33,690
So these are just kind of helpful
colors when you're programming.

494
00:16:33,690 --> 00:16:36,350
So the int and the void,
those are data types.

495
00:16:36,350 --> 00:16:38,080
We'll go over those in a second.

496
00:16:38,080 --> 00:16:39,650
Hi is a string.

497
00:16:39,650 --> 00:16:40,890
But useful colors.

498
00:16:40,890 --> 00:16:44,790
So if you ever accidentally
choose the wrong extension,

499
00:16:44,790 --> 00:16:46,150
you should have these colors.

500
00:16:46,150 --> 00:16:46,650
What's up?

501
00:16:46,650 --> 00:16:50,772
>> STUDENT: How can I copy into a
file [INAUDIBLE] into another file?

502
00:16:50,772 --> 00:16:52,980
JASON HIRSCHHORN: Oh, I'm
going to show you that too.

503
00:16:52,980 --> 00:16:55,070
So copy remove are on the dock.

504
00:16:55,070 --> 00:16:58,300

505
00:16:58,300 --> 00:16:59,070
Let's make this.

506
00:16:59,070 --> 00:17:00,310
Make sure it works.

507
00:17:00,310 --> 00:17:00,960
Make hi.

508
00:17:00,960 --> 00:17:02,430

509
00:17:02,430 --> 00:17:03,610
Works, run it.

510
00:17:03,610 --> 00:17:08,484
So ./hi awesome.

511
00:17:08,484 --> 00:17:09,609
That is your first program.

512
00:17:09,609 --> 00:17:10,800
Let me make it bigger.

513
00:17:10,800 --> 00:17:15,130

514
00:17:15,130 --> 00:17:16,833
So a really good-- Yeah, what's up?

515
00:17:16,833 --> 00:17:18,833
STUDENT: Why would it be
that when I take gedit,

516
00:17:18,833 --> 00:17:21,809
it doesn't give me another
line for gedit hi.txt?

517
00:17:21,809 --> 00:17:23,793

518
00:17:23,793 --> 00:17:25,690
It just puts the cursor to a line.

519
00:17:25,690 --> 00:17:26,273
STUDENT: Yeah.

520
00:17:26,273 --> 00:17:27,265
The [INAUDIBLE].

521
00:17:27,265 --> 00:17:29,520

522
00:17:29,520 --> 00:17:31,510
>> JASON HIRSCHHORN: Wait,
so say that again.

523
00:17:31,510 --> 00:17:35,279
>> STUDENT: When I type gedit, the
first time, the first line--

524
00:17:35,279 --> 00:17:37,070
JASON HIRSCHHORN: Up
there at the very top?

525
00:17:37,070 --> 00:17:39,800
STUDENT: Has no J Harvard
appliance, and the cursor

526
00:17:39,800 --> 00:17:41,237
is just all the way to the left.

527
00:17:41,237 --> 00:17:42,986
JASON HIRSCHHORN: All
the way to the left?

528
00:17:42,986 --> 00:17:43,569
STUDENT: Yeah.

529
00:17:43,569 --> 00:17:44,810
Does anyone else have that?

530
00:17:44,810 --> 00:17:46,920
>> JASON HIRSCHHORN: Oh, well J
Harvard is just like the username.

531
00:17:46,920 --> 00:17:48,770
So that's just the standard username.

532
00:17:48,770 --> 00:17:49,978
>> STUDENT: It stops responding.

533
00:17:49,978 --> 00:17:51,090

534
00:17:51,090 --> 00:17:52,840
JASON HIRSCHHORN: Oh,
it stops responding.

535
00:17:52,840 --> 00:17:55,570
OK, so what you have to do is
you have to close out of gedit.

536
00:17:55,570 --> 00:17:58,360
So close out of gedit,
and it should return.

537
00:17:58,360 --> 00:18:00,726
So is gedit open on your
appliance right now?

538
00:18:00,726 --> 00:18:02,636

539
00:18:02,636 --> 00:18:05,510
If you exit out of it, it should
return and you should be good to go.

540
00:18:05,510 --> 00:18:08,257

541
00:18:08,257 --> 00:18:08,840
Did that work?

542
00:18:08,840 --> 00:18:10,824

543
00:18:10,824 --> 00:18:13,850
>> STUDENT: So did you use
the gedit command to open--

544
00:18:13,850 --> 00:18:16,350
JASON HIRSCHHORN: No, the first
gedit command was a mistake.

545
00:18:16,350 --> 00:18:17,930

546
00:18:17,930 --> 00:18:19,860
The first gedit command,
I to do gedit hi.txt.

547
00:18:19,860 --> 00:18:21,170

548
00:18:21,170 --> 00:18:24,240
So I give it a name, so gedit hi.txt.

549
00:18:24,240 --> 00:18:27,070
hi.txt is the name of the file.

550
00:18:27,070 --> 00:18:28,890
The first one was just
a mistake, and then

551
00:18:28,890 --> 00:18:30,450
I quickly closed out of the program.

552
00:18:30,450 --> 00:18:36,737
So the question was
if I do gedit, I'm not

553
00:18:36,737 --> 00:18:39,320
going to be able to really do
anything else in my command line

554
00:18:39,320 --> 00:18:42,390
until I close that gedit, so I
think that's what they ran into.

555
00:18:42,390 --> 00:18:43,689
So close the gedit.

556
00:18:43,689 --> 00:18:45,730
It'll return out of that
program, and then you'll

557
00:18:45,730 --> 00:18:49,090
be able to actually type
in the command line again.

558
00:18:49,090 --> 00:18:50,290

559
00:18:50,290 --> 00:18:52,198
Is that good?

560
00:18:52,198 --> 00:18:52,698
Dope.

561
00:18:52,698 --> 00:18:57,715

562
00:18:57,715 --> 00:19:00,410
So just make sure to close
it if you run into trouble.

563
00:19:00,410 --> 00:19:01,860

564
00:19:01,860 --> 00:19:04,465
>> OK, so a really good question
a second ago was copying.

565
00:19:04,465 --> 00:19:06,790

566
00:19:06,790 --> 00:19:08,440
So now I have hi.c.

567
00:19:08,440 --> 00:19:09,890
But let's say I want to change it.

568
00:19:09,890 --> 00:19:11,630
I want it to be slightly better.

569
00:19:11,630 --> 00:19:13,250
I want to say hi class.

570
00:19:13,250 --> 00:19:15,670
But I want to keep this template.

571
00:19:15,670 --> 00:19:17,980
I don't have to rewrite
the entire program again.

572
00:19:17,980 --> 00:19:19,700
I want to keep the template.

573
00:19:19,700 --> 00:19:20,480
How do I copy?

574
00:19:20,480 --> 00:19:25,580

575
00:19:25,580 --> 00:19:26,210
>> Easy.

576
00:19:26,210 --> 00:19:29,680
So cp hi.c newhi.c.

577
00:19:29,680 --> 00:19:32,767

578
00:19:32,767 --> 00:19:34,340
Now I have two.

579
00:19:34,340 --> 00:19:48,330
And then I can open up newhi.c,
and instead of just saying hi,

580
00:19:48,330 --> 00:19:51,280
I'll say hi class!

581
00:19:51,280 --> 00:20:00,530

582
00:20:00,530 --> 00:20:01,780
So I'll go back.

583
00:20:01,780 --> 00:20:03,520
Exit out.

584
00:20:03,520 --> 00:20:04,990
Go back to my command line.

585
00:20:04,990 --> 00:20:06,070
ls make newhi.

586
00:20:06,070 --> 00:20:07,500

587
00:20:07,500 --> 00:20:08,140
Run it.

588
00:20:08,140 --> 00:20:09,720

589
00:20:09,720 --> 00:20:10,220
There.

590
00:20:10,220 --> 00:20:11,530
It's better, much better.

591
00:20:11,530 --> 00:20:13,600

592
00:20:13,600 --> 00:20:17,610
So if you want to copy something,
easy as that. cp is copy.

593
00:20:17,610 --> 00:20:22,060

594
00:20:22,060 --> 00:20:25,355
>> So we've gone over moving,
making directories, copying.

595
00:20:25,355 --> 00:20:27,434

596
00:20:27,434 --> 00:20:29,470
Let's see what else should I go over?

597
00:20:29,470 --> 00:20:30,580

598
00:20:30,580 --> 00:20:31,080
Oh, yeah.

599
00:20:31,080 --> 00:20:31,871
Let's go over this.

600
00:20:31,871 --> 00:20:32,990

601
00:20:32,990 --> 00:20:34,300
So this was awesome.

602
00:20:34,300 --> 00:20:35,710

603
00:20:35,710 --> 00:20:37,320
Let's say I wanted to-- oh wait.

604
00:20:37,320 --> 00:20:39,224
I'm going to go back into awesome.

605
00:20:39,224 --> 00:20:41,720

606
00:20:41,720 --> 00:20:46,670
>> Let's say I don't want
these files right here.

607
00:20:46,670 --> 00:20:49,630
Let's say I want them in a new
directory like in directory awesome.

608
00:20:49,630 --> 00:20:51,463
I want to start organizing,
so now I'm going

609
00:20:51,463 --> 00:20:53,390
to have a new directory called hi.

610
00:20:53,390 --> 00:20:55,850
It's got all the programs
I write called hi.

611
00:20:55,850 --> 00:20:57,000
So how do we do that?

612
00:20:57,000 --> 00:21:00,234

613
00:21:00,234 --> 00:21:01,490
>> STUDENT: Change directory.

614
00:21:01,490 --> 00:21:02,448
>> JASON HIRSCHHORN: Yeah.

615
00:21:02,448 --> 00:21:03,077

616
00:21:03,077 --> 00:21:04,070
hi.

617
00:21:04,070 --> 00:21:04,570
Boop.

618
00:21:04,570 --> 00:21:06,910

619
00:21:06,910 --> 00:21:08,370
mkdir hi_dir.

620
00:21:08,370 --> 00:21:13,578

621
00:21:13,578 --> 00:21:16,160
It complained because I
already had a hi in here.

622
00:21:16,160 --> 00:21:17,260

623
00:21:17,260 --> 00:21:18,610
So now I have a hi directory.

624
00:21:18,610 --> 00:21:21,200
So now I want to move everything,
all the programs I wrote,

625
00:21:21,200 --> 00:21:22,950
I want to move them
into the hi directory.

626
00:21:22,950 --> 00:21:24,120
Just clean stuff up.

627
00:21:24,120 --> 00:21:25,245
How do I do that?

628
00:21:25,245 --> 00:21:26,550
>> STUDENT: [INAUDIBLE].

629
00:21:26,550 --> 00:21:28,040
>> JASON HIRSCHHORN: Moving it, right?

630
00:21:28,040 --> 00:21:28,865
So let's move.

631
00:21:28,865 --> 00:21:34,215

632
00:21:34,215 --> 00:21:34,715
Yeah?

633
00:21:34,715 --> 00:21:38,162
>> STUDENT: What's the difference between
hi and hi.c that we already have.

634
00:21:38,162 --> 00:21:39,870
JASON HIRSCHHORN: Oh,
hi.c is the actual.

635
00:21:39,870 --> 00:21:41,770
So that's the file that you wrote.

636
00:21:41,770 --> 00:21:44,670
So if you were going to
open it up in gedit or Nano,

637
00:21:44,670 --> 00:21:46,240
that's what you're typing in.

638
00:21:46,240 --> 00:21:48,710
When you compile it, then
you get an executable file.

639
00:21:48,710 --> 00:21:49,610
That's hi.

640
00:21:49,610 --> 00:21:52,630
So if you opened up hi, that's going
to be a bunch of gibberish to you.

641
00:21:52,630 --> 00:21:57,536
It's basically going to be
bunch of computer instructions.

642
00:21:57,536 --> 00:21:58,036
What's up?

643
00:21:58,036 --> 00:21:59,577
>> STUDENT: What do all the colors mean?

644
00:21:59,577 --> 00:22:00,892
The blue is probably directory.

645
00:22:00,892 --> 00:22:02,010
What's yellow?

646
00:22:02,010 --> 00:22:04,051
>> JASON HIRSCHHORN: Those
are the executable files.

647
00:22:04,051 --> 00:22:08,344
So when I did make hi.c, it
gave me-- so I can do it.

648
00:22:08,344 --> 00:22:09,010
Jumping the gun.

649
00:22:09,010 --> 00:22:11,880
So remove hi yes.

650
00:22:11,880 --> 00:22:12,930
So then let's do ls.

651
00:22:12,930 --> 00:22:13,930
I don't have hi anymore.

652
00:22:13,930 --> 00:22:16,770
So when you make, that's when you
take the program that you wrote

653
00:22:16,770 --> 00:22:18,100
and you make a executable file.

654
00:22:18,100 --> 00:22:20,720
So make hi.c-- well, make hi.

655
00:22:20,720 --> 00:22:21,956

656
00:22:21,956 --> 00:22:24,060
I think he went over this in lecture.

657
00:22:24,060 --> 00:22:25,970
>> These are bunch of
compiler instructions.

658
00:22:25,970 --> 00:22:28,585
So instead of having to actually
write clang with all these.

659
00:22:28,585 --> 00:22:29,860
These are flags.

660
00:22:29,860 --> 00:22:31,210
You just write make.

661
00:22:31,210 --> 00:22:32,680
So this makes the executable files.

662
00:22:32,680 --> 00:22:36,200
So when you do ls, now you have hi.

663
00:22:36,200 --> 00:22:38,320
So this is what you're
going to actually run.

664
00:22:38,320 --> 00:22:45,130
And so you run that by doing
./hi, and it runs your program.

665
00:22:45,130 --> 00:22:51,066
But if I try to do that with
hi.c, no, it's not going to work.

666
00:22:51,066 --> 00:22:52,190
Yeah, does that make sense?

667
00:22:52,190 --> 00:22:52,990
>> STUDENT: Mm-hm.

668
00:22:52,990 --> 00:22:53,948
>> JASON HIRSCHHORN: Cool.

669
00:22:53,948 --> 00:22:55,632

670
00:22:55,632 --> 00:22:57,330
Wait, I wanted to say something else.

671
00:22:57,330 --> 00:22:58,450

672
00:22:58,450 --> 00:23:02,226
Just real quick, in case
anyone is interested,

673
00:23:02,226 --> 00:23:04,350
when you jump out of a
directory, it's the dot dot.

674
00:23:04,350 --> 00:23:05,580

675
00:23:05,580 --> 00:23:08,960
Does anybody have an idea of what
maybe just the singular dot means?

676
00:23:08,960 --> 00:23:15,085

677
00:23:15,085 --> 00:23:15,960
STUDENT: [INAUDIBLE].

678
00:23:15,960 --> 00:23:16,631

679
00:23:16,631 --> 00:23:18,880
JASON HIRSCHHORN: It's
actually the current directory.

680
00:23:18,880 --> 00:23:20,730
So it's your current directory.

681
00:23:20,730 --> 00:23:21,920

682
00:23:21,920 --> 00:23:22,610
So I'm here.

683
00:23:22,610 --> 00:23:23,700
I'm in awesome.

684
00:23:23,700 --> 00:23:27,090
If I do cd dot, it doesn't do anything.

685
00:23:27,090 --> 00:23:28,750
It takes me to my current directory.

686
00:23:28,750 --> 00:23:34,407
So a little redundant, but you have
to do that, so ./ your program name,

687
00:23:34,407 --> 00:23:36,490
in order to run your
program, you have to do that.

688
00:23:36,490 --> 00:23:38,020

689
00:23:38,020 --> 00:23:38,520
OK.

690
00:23:38,520 --> 00:23:39,555

691
00:23:39,555 --> 00:23:42,032
>> STUDENT: If you do cd dot
dot dot, however many dots

692
00:23:42,032 --> 00:23:43,990
will it just take you up
that many directories?

693
00:23:43,990 --> 00:23:46,527
>> JASON HIRSCHHORN: You mean
like cd dot dot dot dot?

694
00:23:46,527 --> 00:23:47,110
STUDENT: Yeah.

695
00:23:47,110 --> 00:23:47,985
JASON HIRSCHHORN: No.

696
00:23:47,985 --> 00:23:48,850

697
00:23:48,850 --> 00:23:52,130
So actually Remember I did ls -l?

698
00:23:52,130 --> 00:23:53,290

699
00:23:53,290 --> 00:23:56,800
If I do something else, I can ls -a.

700
00:23:56,800 --> 00:23:59,940
So what this says is -a
shows you everything.

701
00:23:59,940 --> 00:24:03,180
So it shows you things that are
hidden and things that aren't hidden.

702
00:24:03,180 --> 00:24:10,880
So if you notice that when I did
just ls, I just saw that stuff,

703
00:24:10,880 --> 00:24:12,060
the stuff I made.

704
00:24:12,060 --> 00:24:14,640
If I do -a, it's going
to show me everything.

705
00:24:14,640 --> 00:24:18,460
And so current directory,
directory above it.

706
00:24:18,460 --> 00:24:22,025

707
00:24:22,025 --> 00:24:22,900
Does that make sense?

708
00:24:22,900 --> 00:24:23,130
Yeah?

709
00:24:23,130 --> 00:24:25,296
>> STUDENT: But those aren't
actually in the directory.

710
00:24:25,296 --> 00:24:30,938
The current directory isn't in itself,
so why show those with dots inside?

711
00:24:30,938 --> 00:24:33,910
>> JASON HIRSCHHORN: You mean it's
like it's not in the directory.

712
00:24:33,910 --> 00:24:34,810
>> STUDENT: Right.

713
00:24:34,810 --> 00:24:36,620
So we have a list of things
that are in the directory.

714
00:24:36,620 --> 00:24:37,630
>> JASON HIRSCHHORN: I think
it is in the directory.

715
00:24:37,630 --> 00:24:41,190
Like -a shows everything, even if
it's hidden inside the directory.

716
00:24:41,190 --> 00:24:44,440
So I think it's just a route to the
current directory if that makes sense.

717
00:24:44,440 --> 00:24:46,400

718
00:24:46,400 --> 00:24:47,400
It's a little recursive.

719
00:24:47,400 --> 00:24:48,300
It's like Inception.

720
00:24:48,300 --> 00:24:48,920
What's up?

721
00:24:48,920 --> 00:24:52,090
>> STUDENT: So you said
-a shows [INAUDIBLE]?

722
00:24:52,090 --> 00:24:53,215
JASON HIRSCHHORN: -a, yeah.

723
00:24:53,215 --> 00:24:54,964

724
00:24:54,964 --> 00:24:56,572
>> STUDENT: What makes it [INAUDIBLE]?

725
00:24:56,572 --> 00:24:59,280
JASON HIRSCHHORN: Well, for example,
let's go back up to the top.

726
00:24:59,280 --> 00:25:00,890

727
00:25:00,890 --> 00:25:04,180
It's usually stuff you shouldn't mess
with and you don't need to worry about.

728
00:25:04,180 --> 00:25:07,180
So this is kind of the home.

729
00:25:07,180 --> 00:25:10,230
If I do -a, I get tons of stuff.

730
00:25:10,230 --> 00:25:14,760

731
00:25:14,760 --> 00:25:15,440
All that stuff.

732
00:25:15,440 --> 00:25:18,840

733
00:25:18,840 --> 00:25:21,258
And you don't need to mess
with any of that stuff.

734
00:25:21,258 --> 00:25:23,716
Definitely don't start going
in here and just remove stuff.

735
00:25:23,716 --> 00:25:27,190
>> [LAUGHTER]

736
00:25:27,190 --> 00:25:32,440
>> Yeah, this was a little bit more
comfy stuff, but it's good to know.

737
00:25:32,440 --> 00:25:34,310
I think it's good to know.

738
00:25:34,310 --> 00:25:35,540

739
00:25:35,540 --> 00:25:41,420
But if you never want to type -a
in the entirety of this course,

740
00:25:41,420 --> 00:25:42,540
just forget it.

741
00:25:42,540 --> 00:25:43,040
What's up?

742
00:25:43,040 --> 00:25:44,436
>> STUDENT: What is the ls -l?

743
00:25:44,436 --> 00:25:46,310
JASON HIRSCHHORN: That
shows you permissions.

744
00:25:46,310 --> 00:25:50,269
Basically you use that
for permissions, so -l.

745
00:25:50,269 --> 00:25:52,060
It shows you a little
bit more information,

746
00:25:52,060 --> 00:25:54,840
but again, this is a little
bit more comfy stuff.

747
00:25:54,840 --> 00:25:56,040
These are just permissions.

748
00:25:56,040 --> 00:25:57,710
So the permissions of the folders.

749
00:25:57,710 --> 00:26:04,459
So just for example, let's say I made a
folder, so the d represents directory.

750
00:26:04,459 --> 00:26:05,500
So those are directories.

751
00:26:05,500 --> 00:26:08,250
And then read, write, execute.

752
00:26:08,250 --> 00:26:12,610
So those are permissions for
I think user, group, world.

753
00:26:12,610 --> 00:26:14,490

754
00:26:14,490 --> 00:26:15,610
Totally going too far.

755
00:26:15,610 --> 00:26:18,580
You're going to go in this like
weeks from now, but just so you know,

756
00:26:18,580 --> 00:26:19,340
those are permissions.

757
00:26:19,340 --> 00:26:19,840
What's up?

758
00:26:19,840 --> 00:26:23,189
STUDENT: Can you clear rather than
just skip to the next thing, can you--

759
00:26:23,189 --> 00:26:24,980
JASON HIRSCHHORN: You
mean actually delete?

760
00:26:24,980 --> 00:26:25,859

761
00:26:25,859 --> 00:26:26,400
I don't know.

762
00:26:26,400 --> 00:26:27,450
I never do that.

763
00:26:27,450 --> 00:26:28,700
Why would you want to do that?

764
00:26:28,700 --> 00:26:29,782

765
00:26:29,782 --> 00:26:30,698
Why would you do that?

766
00:26:30,698 --> 00:26:32,330

767
00:26:32,330 --> 00:26:32,840
I like it.

768
00:26:32,840 --> 00:26:34,020
You live on the edge.

769
00:26:34,020 --> 00:26:35,561
You're like I don't want any of this.

770
00:26:35,561 --> 00:26:40,380

771
00:26:40,380 --> 00:26:41,096
That's intense.

772
00:26:41,096 --> 00:26:41,970
STUDENT: [INAUDIBLE].

773
00:26:41,970 --> 00:26:43,541

774
00:26:43,541 --> 00:26:45,165
JASON HIRSCHHORN: Yeah, we can do that.

775
00:26:45,165 --> 00:26:47,960

776
00:26:47,960 --> 00:26:52,667
Sorry, messing with the size is
totally freaking me out right now.

777
00:26:52,667 --> 00:26:53,920

778
00:26:53,920 --> 00:26:54,950
Let's go up.

779
00:26:54,950 --> 00:26:56,759
Yeah, so now I can't go up anymore.

780
00:26:56,759 --> 00:26:58,550
So everything I taught
you is gone forever.

781
00:26:58,550 --> 00:26:59,050
Thank you.

782
00:26:59,050 --> 00:27:04,311

783
00:27:04,311 --> 00:27:05,310
We made our directories.

784
00:27:05,310 --> 00:27:08,268
We made our files and stuff like
that, so we still have all that stuff.

785
00:27:08,268 --> 00:27:10,270

786
00:27:10,270 --> 00:27:11,200
OK, I'll go fast.

787
00:27:11,200 --> 00:27:13,300

788
00:27:13,300 --> 00:27:14,100
>> So real quick.

789
00:27:14,100 --> 00:27:15,520
So let's say I'm in awesome.

790
00:27:15,520 --> 00:27:17,480

791
00:27:17,480 --> 00:27:20,090
Let's say I wanted to move
everything to the new directory

792
00:27:20,090 --> 00:27:21,600
because I just want
to organize it, right?

793
00:27:21,600 --> 00:27:22,560
So how would I do that.

794
00:27:22,560 --> 00:27:23,650

795
00:27:23,650 --> 00:27:24,150
Move.

796
00:27:24,150 --> 00:27:25,399
We're going to use move again.

797
00:27:25,399 --> 00:27:26,320
So move hi.c.

798
00:27:26,320 --> 00:27:27,620

799
00:27:27,620 --> 00:27:29,810
And what you can do is
you start listing stuff,

800
00:27:29,810 --> 00:27:32,268
and the last thing you list is
where it's going to move it.

801
00:27:32,268 --> 00:27:38,230
So move hi.c, hi newhi newhi.c, hi_dir.

802
00:27:38,230 --> 00:27:41,960

803
00:27:41,960 --> 00:27:45,880
And so it moved everything into
the last thing you mentioned.

804
00:27:45,880 --> 00:27:49,462
So then change directory, hi_dir ls.

805
00:27:49,462 --> 00:27:50,420
Everything is in there.

806
00:27:50,420 --> 00:27:52,625
So it's nice and more organized.

807
00:27:52,625 --> 00:27:53,970

808
00:27:53,970 --> 00:27:57,330
>> OK, let's say I hate
my original hi program.

809
00:27:57,330 --> 00:27:58,700
I want to get rid of it.

810
00:27:58,700 --> 00:28:00,380
How do I get rid of it?

811
00:28:00,380 --> 00:28:00,880
What's up?

812
00:28:00,880 --> 00:28:01,755
>> STUDENT: [INAUDIBLE].

813
00:28:01,755 --> 00:28:04,977

814
00:28:04,977 --> 00:28:08,060
JASON HIRSCHHORN: Let's say I just
want to remove the program, so just hi.

815
00:28:08,060 --> 00:28:11,122

816
00:28:11,122 --> 00:28:11,830
No, you're right.

817
00:28:11,830 --> 00:28:14,680
So it's rm, but you do rm hi.

818
00:28:14,680 --> 00:28:18,224

819
00:28:18,224 --> 00:28:19,890
It's going to give you a little warning.

820
00:28:19,890 --> 00:28:25,440
It's going to say are you sure you
want to delete this, and yes I do.

821
00:28:25,440 --> 00:28:27,190
If you don't want to
be prompted like that

822
00:28:27,190 --> 00:28:34,260
because you don't have time
for warnings, remove -f.

823
00:28:34,260 --> 00:28:35,720
This is another flag.

824
00:28:35,720 --> 00:28:36,910
It's like the -l.

825
00:28:36,910 --> 00:28:38,190
It's like the -a.

826
00:28:38,190 --> 00:28:40,610
These are just flags that
you're giving to these commands.

827
00:28:40,610 --> 00:28:41,490
So remove -f.

828
00:28:41,490 --> 00:28:42,540

829
00:28:42,540 --> 00:28:44,340
-f f means force.

830
00:28:44,340 --> 00:28:45,670
So force it.

831
00:28:45,670 --> 00:28:47,390
I do not want to be prompted.

832
00:28:47,390 --> 00:28:48,560
So remove -f.

833
00:28:48,560 --> 00:28:49,920

834
00:28:49,920 --> 00:28:50,720
Let's do hi.c.

835
00:28:50,720 --> 00:28:53,589

836
00:28:53,589 --> 00:28:54,380
Just got rid of it.

837
00:28:54,380 --> 00:28:55,130
It didn't tell me.

838
00:28:55,130 --> 00:28:56,160

839
00:28:56,160 --> 00:28:59,270
>> But let's say instead I'm
done with this directory.

840
00:28:59,270 --> 00:29:01,010
I want to get rid of directory.

841
00:29:01,010 --> 00:29:02,950
So I do remove hi_dir.

842
00:29:02,950 --> 00:29:04,124

843
00:29:04,124 --> 00:29:05,040
No, that doesn't work.

844
00:29:05,040 --> 00:29:11,170

845
00:29:11,170 --> 00:29:13,685
No, so it won't let
me remove a directory.

846
00:29:13,685 --> 00:29:15,770

847
00:29:15,770 --> 00:29:17,010
Does anybody have an idea?

848
00:29:17,010 --> 00:29:18,752
>> STUDENT: Is it remove dir?

849
00:29:18,752 --> 00:29:20,335
JASON HIRSCHHORN: So remove like this?

850
00:29:20,335 --> 00:29:24,961

851
00:29:24,961 --> 00:29:26,398
>> STUDENT: No.

852
00:29:26,398 --> 00:29:27,835
Just the [INAUDIBLE].

853
00:29:27,835 --> 00:29:29,024

854
00:29:29,024 --> 00:29:30,940
JASON HIRSCHHORN: No,
right now there's no hi.

855
00:29:30,940 --> 00:29:32,099
There's just hi_dir.

856
00:29:32,099 --> 00:29:33,140
So this is the directory.

857
00:29:33,140 --> 00:29:34,730

858
00:29:34,730 --> 00:29:37,930
So actually what you want to do
is-- oh, do you have an idea?

859
00:29:37,930 --> 00:29:39,281
I see like a half hand.

860
00:29:39,281 --> 00:29:40,156
>> STUDENT: [INAUDIBLE].

861
00:29:40,156 --> 00:29:41,215

862
00:29:41,215 --> 00:29:42,090
JASON HIRSCHHORN: OK.

863
00:29:42,090 --> 00:29:43,232

864
00:29:43,232 --> 00:29:44,470
>> STUDENT: [INAUDIBLE].

865
00:29:44,470 --> 00:29:45,345
>> JASON HIRSCHHORN: OK.

866
00:29:45,345 --> 00:29:48,200

867
00:29:48,200 --> 00:29:51,790
So if I want to remove
a directory, remove -r.

868
00:29:51,790 --> 00:29:52,580
That's recursive.

869
00:29:52,580 --> 00:29:54,230
So remove that directory recursive.

870
00:29:54,230 --> 00:29:57,700
So I want you to go into that directory,
remove everything in the directory,

871
00:29:57,700 --> 00:29:59,180
and then get rid of the directory.

872
00:29:59,180 --> 00:30:00,930
And then I'm going to
f as well, because I

873
00:30:00,930 --> 00:30:04,680
don't want it to prompt me with warnings
after it removes every single file.

874
00:30:04,680 --> 00:30:06,720
So remove -rf hi_dir.

875
00:30:06,720 --> 00:30:08,680

876
00:30:08,680 --> 00:30:09,540
Boom, it's gone.

877
00:30:09,540 --> 00:30:10,582

878
00:30:10,582 --> 00:30:12,040
Just be careful where you use that.

879
00:30:12,040 --> 00:30:14,730
I'm going to use it
here too. -rf awesome.

880
00:30:14,730 --> 00:30:16,800

881
00:30:16,800 --> 00:30:17,530
It's gone.

882
00:30:17,530 --> 00:30:18,780
Be careful where you use that.

883
00:30:18,780 --> 00:30:22,990
If you use that here and type something
like this, don't ever do that.

884
00:30:22,990 --> 00:30:26,200
That will delete everything on your
appliance without ever warning you.

885
00:30:26,200 --> 00:30:27,670
And I've done that.

886
00:30:27,670 --> 00:30:31,620
Grading problem sets at 4:00 AM, I was
trying remove problem set directories,

887
00:30:31,620 --> 00:30:32,320
and I did this.

888
00:30:32,320 --> 00:30:34,080
And I was like oh my god.

889
00:30:34,080 --> 00:30:35,170

890
00:30:35,170 --> 00:30:36,850
Don't do-- I tried to cancel it.

891
00:30:36,850 --> 00:30:38,000
You can cancel.

892
00:30:38,000 --> 00:30:42,670
Command C just cancels everything,
but I already deleted like 75%.

893
00:30:42,670 --> 00:30:45,570
So I ruined it.

894
00:30:45,570 --> 00:30:46,580
And people do that.

895
00:30:46,580 --> 00:30:47,620
Everyone does this.

896
00:30:47,620 --> 00:30:49,460
Don't do this though this semester.

897
00:30:49,460 --> 00:30:49,960
It sucks.

898
00:30:49,960 --> 00:30:52,330

899
00:30:52,330 --> 00:30:54,050
I'm nervous having it here.

900
00:30:54,050 --> 00:30:55,247
I'm going to delete it.

901
00:30:55,247 --> 00:30:58,354
>> [LAUGHTER]

902
00:30:58,354 --> 00:30:59,020
Can you imagine?

903
00:30:59,020 --> 00:31:01,050

904
00:31:01,050 --> 00:31:02,450
OK, questions.

905
00:31:02,450 --> 00:31:03,138
Yes?

906
00:31:03,138 --> 00:31:09,114
>> STUDENT: So if we do everything
you're doing here, is this the same

907
00:31:09,114 --> 00:31:13,791
as just going into actually
file save as [INAUDIBLE].

908
00:31:13,791 --> 00:31:16,530

909
00:31:16,530 --> 00:31:18,405
JASON HIRSCHHORN: Oh,
you mean through gedit.

910
00:31:18,405 --> 00:31:18,870
STUDENT: Yeah.

911
00:31:18,870 --> 00:31:20,078
JASON HIRSCHHORN: Yeah it is.

912
00:31:20,078 --> 00:31:21,094

913
00:31:21,094 --> 00:31:21,760
gedit is useful.

914
00:31:21,760 --> 00:31:23,440

915
00:31:23,440 --> 00:31:24,730
So gedit is very useful.

916
00:31:24,730 --> 00:31:26,550
In this class, you can do a
lot of things through gedit.

917
00:31:26,550 --> 00:31:27,260
You can save.

918
00:31:27,260 --> 00:31:27,980
You can rename.

919
00:31:27,980 --> 00:31:34,170
You can move files and stuff like that,
but just truthfully when you go to 50--

920
00:31:34,170 --> 00:31:40,330
well you are in 50-- 51, if you go
into 61, this is going to be your life.

921
00:31:40,330 --> 00:31:41,590
This is the command line.

922
00:31:41,590 --> 00:31:44,220
This is where you will program
for the rest of your life,

923
00:31:44,220 --> 00:31:47,050
so definitely use gedit if you want.

924
00:31:47,050 --> 00:31:47,929

925
00:31:47,929 --> 00:31:49,220
Definitely a good way to start.

926
00:31:49,220 --> 00:31:52,550
For the first problem sets, definitely
use, but every once in a while

927
00:31:52,550 --> 00:31:56,790
try to get more used more comfortable
with command line arguments.

928
00:31:56,790 --> 00:31:58,230
But you can, definitely.

929
00:31:58,230 --> 00:31:58,730
What's up?

930
00:31:58,730 --> 00:32:01,660
>> STUDENT: So when we want to delete
one of the files we've made,

931
00:32:01,660 --> 00:32:04,426
there are two ways. [INAUDIBLE].

932
00:32:04,426 --> 00:32:06,385
Is there a way when you're
deleting a directory

933
00:32:06,385 --> 00:32:08,467
to ask for prompt so you
don't end up deleting it?

934
00:32:08,467 --> 00:32:09,610
JASON HIRSCHHORN: rm -r.

935
00:32:09,610 --> 00:32:10,810
So don't force it.

936
00:32:10,810 --> 00:32:11,489
So rm -r.

937
00:32:11,489 --> 00:32:14,280
It's going to go through recursively,
delete everything, prompt you

938
00:32:14,280 --> 00:32:17,340
after everything, which
will drive you nuts.

939
00:32:17,340 --> 00:32:18,660

940
00:32:18,660 --> 00:32:24,060
Like I almost exclusively do rm
-f and rm -rf, just constantly.

941
00:32:24,060 --> 00:32:26,298
I'm like I don't have time.

942
00:32:26,298 --> 00:32:27,600
I'm a busy man.

943
00:32:27,600 --> 00:32:28,580
All right, what's up?

944
00:32:28,580 --> 00:32:29,170
Yeah.

945
00:32:29,170 --> 00:32:32,015
>> STUDENT: Is there an undo, or a
trash bin, or anything like that?

946
00:32:32,015 --> 00:32:32,890
JASON HIRSCHHORN: No.

947
00:32:32,890 --> 00:32:35,120
[LAUGHTER]

948
00:32:35,120 --> 00:32:39,100
I could go back and get my
appliance that I just deleted, no.

949
00:32:39,100 --> 00:32:39,600
No, no, no.

950
00:32:39,600 --> 00:32:41,390

951
00:32:41,390 --> 00:32:43,030
If you do rm, it should be gone.

952
00:32:43,030 --> 00:32:43,963
What's up?

953
00:32:43,963 --> 00:32:46,785
>> STUDENT: So you can
[INAUDIBLE] together.

954
00:32:46,785 --> 00:32:48,410
JASON HIRSCHHORN: Yeah, just like that.

955
00:32:48,410 --> 00:32:52,190
So for example, you saw the rm -rf.

956
00:32:52,190 --> 00:32:55,700
Let's say I want to
do ls -la, it shows me

957
00:32:55,700 --> 00:33:00,120
everything, even hidden
things with their permissions.

958
00:33:00,120 --> 00:33:02,160

959
00:33:02,160 --> 00:33:06,762
>> STUDENT: So then r, the -r
flag, if we don't have that,

960
00:33:06,762 --> 00:33:08,250
we can't delete a directory, right?

961
00:33:08,250 --> 00:33:08,746
>> JASON HIRSCHHORN: Right.

962
00:33:08,746 --> 00:33:10,990
>> STUDENT: So that says that we want
to do something with the directory?

963
00:33:10,990 --> 00:33:12,610
Is that what that means?

964
00:33:12,610 --> 00:33:14,570
>> JASON HIRSCHHORN: -r means recursively.

965
00:33:14,570 --> 00:33:17,670
So a directory is going to
have files in it, right?

966
00:33:17,670 --> 00:33:21,680
So what you want to do is you
want to go into that directory,

967
00:33:21,680 --> 00:33:24,110
delete everything, all the
files in that directory,

968
00:33:24,110 --> 00:33:26,510
then pop out and delete
the actual directory.

969
00:33:26,510 --> 00:33:30,660
So the -r means recursive, do it
all recursively if that makes sense.

970
00:33:30,660 --> 00:33:31,160
Yeah.

971
00:33:31,160 --> 00:33:34,160
>> STUDENT: So directories have
[INAUDIBLE] and just delete it.

972
00:33:34,160 --> 00:33:35,160
Or do you still--

973
00:33:35,160 --> 00:33:36,326
>> JASON HIRSCHHORN: Let's try.

974
00:33:36,326 --> 00:33:39,040

975
00:33:39,040 --> 00:33:40,955
So mkdir empty.

976
00:33:40,955 --> 00:33:42,320

977
00:33:42,320 --> 00:33:43,810
Remove empty.

978
00:33:43,810 --> 00:33:44,374
No.

979
00:33:44,374 --> 00:33:45,646
>> STUDENT: No, so you still need the--

980
00:33:45,646 --> 00:33:46,937
>> JASON HIRSCHHORN: Yeah, always.

981
00:33:46,937 --> 00:33:48,940
So -r, -rf, empty.

982
00:33:48,940 --> 00:33:50,432

983
00:33:50,432 --> 00:33:51,734
Awesome.

984
00:33:51,734 --> 00:33:52,685
Anymore questions?

985
00:33:52,685 --> 00:33:54,290

986
00:33:54,290 --> 00:33:59,230
I think that is your crash
course on command line stuff.

987
00:33:59,230 --> 00:34:02,560
Any questions, because we're going to
jump over to data types, and loops,

988
00:34:02,560 --> 00:34:03,901
and all that stuff?

989
00:34:03,901 --> 00:34:04,400
What's up?

990
00:34:04,400 --> 00:34:07,960
>> STUDENT: I don't have CS50
showing as one of my directories.

991
00:34:07,960 --> 00:34:09,370
Is that normal?

992
00:34:09,370 --> 00:34:09,710
>> JASON HIRSCHHORN: Oh, yeah.

993
00:34:09,710 --> 00:34:10,929
That's mine.

994
00:34:10,929 --> 00:34:14,830
Yeah, that's where my
solutions to your stuff is.

995
00:34:14,830 --> 00:34:17,670
>> [LAUGHTER]

996
00:34:17,670 --> 00:34:20,469
>> So yeah, that's absolutely normal.

997
00:34:20,469 --> 00:34:23,870
I think you'll probably
just have these four.

998
00:34:23,870 --> 00:34:25,130
I think that might be normal.

999
00:34:25,130 --> 00:34:25,630
Yeah.

1000
00:34:25,630 --> 00:34:27,370

1001
00:34:27,370 --> 00:34:28,730
OK, any more questions?

1002
00:34:28,730 --> 00:34:30,219
I know that was super fast.

1003
00:34:30,219 --> 00:34:30,830
What's up?

1004
00:34:30,830 --> 00:34:33,788
>> STUDENT: I saw the blue green color.

1005
00:34:33,788 --> 00:34:34,780
What is that?

1006
00:34:34,780 --> 00:34:36,405
>> JASON HIRSCHHORN: That means directory.

1007
00:34:36,405 --> 00:34:36,905

1008
00:34:36,905 --> 00:34:38,000
STUDENT: And this blue?

1009
00:34:38,000 --> 00:34:40,100
>> JASON HIRSCHHORN: Oh,
you mean this blue green?

1010
00:34:40,100 --> 00:34:41,290
>> STUDENT: No.

1011
00:34:41,290 --> 00:34:41,724
>> JASON HIRSCHHORN: This blue green?

1012
00:34:41,724 --> 00:34:42,434
>> STUDENT: No.

1013
00:34:42,434 --> 00:34:43,195
When you listed--

1014
00:34:43,195 --> 00:34:44,070
JASON HIRSCHHORN: Oh.

1015
00:34:44,070 --> 00:34:47,100

1016
00:34:47,100 --> 00:34:47,620
Like this?

1017
00:34:47,620 --> 00:34:49,000
>> STUDENT: Yes, the icons.

1018
00:34:49,000 --> 00:34:50,125
>> JASON HIRSCHHORN: Oh, this.

1019
00:34:50,125 --> 00:34:50,678

1020
00:34:50,678 --> 00:34:51,219
I don't know.

1021
00:34:51,219 --> 00:34:52,052
What does that mean?

1022
00:34:52,052 --> 00:34:58,330

1023
00:34:58,330 --> 00:35:00,100
So it seems to be
pointing to a directory.

1024
00:35:00,100 --> 00:35:02,240
>> STUDENT: It almost looks like an alias.

1025
00:35:02,240 --> 00:35:03,594
>> JASON HIRSCHHORN: It might be.

1026
00:35:03,594 --> 00:35:04,760
You don't need to know that.

1027
00:35:04,760 --> 00:35:11,205

1028
00:35:11,205 --> 00:35:11,955
Anymore questions?

1029
00:35:11,955 --> 00:35:14,180

1030
00:35:14,180 --> 00:35:14,680
Awesome.

1031
00:35:14,680 --> 00:35:16,900
If you have any questions,
I know that was a lot.

1032
00:35:16,900 --> 00:35:18,190
A lot of this information
will be online.

1033
00:35:18,190 --> 00:35:19,750
I'll put it online for you guys.

1034
00:35:19,750 --> 00:35:21,187
Section B will be online as well.

1035
00:35:21,187 --> 00:35:23,270
Or if you have questions,
just come up and ask me.

1036
00:35:23,270 --> 00:35:30,660

1037
00:35:30,660 --> 00:35:32,142
Here you go.

1038
00:35:32,142 --> 00:35:41,050

1039
00:35:41,050 --> 00:35:44,400
So now Sharon and
Hannah will go over some

1040
00:35:44,400 --> 00:35:46,720
of the logic behind problem set one.

1041
00:35:46,720 --> 00:35:53,266

1042
00:35:53,266 --> 00:35:54,250
>> SHARON: Oh my god.

1043
00:35:54,250 --> 00:35:56,218

1044
00:35:56,218 --> 00:35:57,694
Troubles.

1045
00:35:57,694 --> 00:35:59,170
>> HANNAH: In the meantime, I'm Hanna.

1046
00:35:59,170 --> 00:36:00,154
This is Sharon.

1047
00:36:00,154 --> 00:36:03,106
We are both CS50 TFs, and
we're going to give you

1048
00:36:03,106 --> 00:36:06,050
a little intro on a couple important
things for problem set one.

1049
00:36:06,050 --> 00:36:09,670
Everything from data types
to conditionals to for loops.

1050
00:36:09,670 --> 00:36:10,620
Loops in general.

1051
00:36:10,620 --> 00:36:14,360
>> SHARON: And in the end, we
will take a look at P set one,

1052
00:36:14,360 --> 00:36:16,739
and what you have to know for it.

1053
00:36:16,739 --> 00:36:18,030
So let's start with data types.

1054
00:36:18,030 --> 00:36:19,840

1055
00:36:19,840 --> 00:36:23,230
You guys should be familiar with the
ones that are highlighted in blue.

1056
00:36:23,230 --> 00:36:25,340
So we can start with ints.

1057
00:36:25,340 --> 00:36:31,500
ints are integers, so one, two,
three, four. floats, floating points.

1058
00:36:31,500 --> 00:36:37,830
Like integers with decimals,
so 5.2 or even 5.0.

1059
00:36:37,830 --> 00:36:44,230
Chars are characters like A, B, C.
And a string, you guys all know.

1060
00:36:44,230 --> 00:36:48,470
Like CS50 or hello and world.

1061
00:36:48,470 --> 00:36:50,290

1062
00:36:50,290 --> 00:36:56,890
>> Bool is a Boolean, so we have
true and false as our Boolean.

1063
00:36:56,890 --> 00:37:01,550
So if something computes to truth--
5 equals 5, that computes to true,

1064
00:37:01,550 --> 00:37:06,470
and if we have 5 equals 4, that's
false, so that computes to false.

1065
00:37:06,470 --> 00:37:12,280
And here we have the associated
size of all of these data types.

1066
00:37:12,280 --> 00:37:14,860
And you will have to know
this for your quizzes,

1067
00:37:14,860 --> 00:37:18,412
so this might be helpful to
remember, but we'll post these.

1068
00:37:18,412 --> 00:37:19,745
Actually they're already posted.

1069
00:37:19,745 --> 00:37:21,921

1070
00:37:21,921 --> 00:37:24,420
So you should be familiar with
the ones highlighted in blue.

1071
00:37:24,420 --> 00:37:27,900

1072
00:37:27,900 --> 00:37:30,580
>> JASON HIRSCHHORN: Real
quick, just in case you

1073
00:37:30,580 --> 00:37:34,096
want to know the difference
between a char and a string.

1074
00:37:34,096 --> 00:37:45,020
So when you're writing stuff,
whenever you have something like "hi,"

1075
00:37:45,020 --> 00:37:46,340
that's going to be a string.

1076
00:37:46,340 --> 00:37:48,090
So if there are two
quotes, it's a string.

1077
00:37:48,090 --> 00:37:52,890
But if I were to an "h"
like that, that's a string.

1078
00:37:52,890 --> 00:37:55,759
But if I only have one
quote, that's a char.

1079
00:37:55,759 --> 00:37:57,550
And so what's the
difference you might ask.

1080
00:37:57,550 --> 00:38:00,985
Well, the difference is
this is one byte of memory.

1081
00:38:00,985 --> 00:38:02,265
This is 4 bytes of memory.

1082
00:38:02,265 --> 00:38:09,480

1083
00:38:09,480 --> 00:38:10,520
>> SHARON: float?

1084
00:38:10,520 --> 00:38:12,180
Describe it again?

1085
00:38:12,180 --> 00:38:18,200
OK, it's kind of like a number
that has a decimal point with it,

1086
00:38:18,200 --> 00:38:27,569
so 5.2 or even 5.0 is a float
versus just 5 is an int.

1087
00:38:27,569 --> 00:38:28,444
STUDENT: [INAUDIBLE].

1088
00:38:28,444 --> 00:38:30,240

1089
00:38:30,240 --> 00:38:36,301
>> SHARON: Oh, it can have many
decimal points, so 5.675 to 3.1415.

1090
00:38:36,301 --> 00:38:36,800
Yes?

1091
00:38:36,800 --> 00:38:39,716
>> STUDENT: Do we need to know
all the sizes for this?

1092
00:38:39,716 --> 00:38:40,216
SHARON: Yes.

1093
00:38:40,216 --> 00:38:41,293

1094
00:38:41,293 --> 00:38:42,168
STUDENT: [INAUDIBLE].

1095
00:38:42,168 --> 00:38:45,810

1096
00:38:45,810 --> 00:38:49,250
>> SHARON: You don't worry about
the white ones just yet.

1097
00:38:49,250 --> 00:38:54,349
>> HANNAH: The notes are
posted at CS50.net/sections.

1098
00:38:54,349 --> 00:38:56,432
STUDENT: Just out of
curiosity, is there a utility

1099
00:38:56,432 --> 00:39:00,424
to knowing the size of the files you're
calling so that we should know it?

1100
00:39:00,424 --> 00:39:01,430

1101
00:39:01,430 --> 00:39:04,330
>> SHARON: So these are
the data types, but yes.

1102
00:39:04,330 --> 00:39:09,820
So in this case, which one would
take up more memory or more space?

1103
00:39:09,820 --> 00:39:13,940
>> JASON HIRSCHHORN: So
for a concrete example,

1104
00:39:13,940 --> 00:39:16,904
in I think problem set
four or five, we're

1105
00:39:16,904 --> 00:39:19,070
going to give you a bunch
of data, and you basically

1106
00:39:19,070 --> 00:39:20,710
have to traverse that data.

1107
00:39:20,710 --> 00:39:24,470
So it's useful to know that
if you have so many integers,

1108
00:39:24,470 --> 00:39:25,770
that's going to be what.

1109
00:39:25,770 --> 00:39:28,802
So let's say I gave you ten
integers, what's the size of that?

1110
00:39:28,802 --> 00:39:30,111

1111
00:39:30,111 --> 00:39:30,610
STUDENT: 40.

1112
00:39:30,610 --> 00:39:32,026
JASON HIRSCHHORN: 40 bytes, right.

1113
00:39:32,026 --> 00:39:35,690
So you might need to know that
OK, I need to jump 40 bytes.

1114
00:39:35,690 --> 00:39:42,200
So let's say instead it's 40 chars,
then-- let's say I gave you 10 chars,

1115
00:39:42,200 --> 00:39:44,860
then you know, OK, I only
need to jump 10 bytes.

1116
00:39:44,860 --> 00:39:47,651
So it's very useful to know the
size of the actual data types,

1117
00:39:47,651 --> 00:39:49,900
because a lot times you'll
be jumping around the data,

1118
00:39:49,900 --> 00:39:51,399
so you need to know how far to jump.

1119
00:39:51,399 --> 00:39:53,854

1120
00:39:53,854 --> 00:39:56,780
>> STUDENT: What's the difference
between the quotes and one quote?

1121
00:39:56,780 --> 00:39:58,670
>> JASON HIRSCHHORN: OK,
two quotes is a string.

1122
00:39:58,670 --> 00:40:00,423
One quote is a char.

1123
00:40:00,423 --> 00:40:03,570
>> STUDENT: Like operationally,
what's the difference?

1124
00:40:03,570 --> 00:40:04,466
They both say hi.

1125
00:40:04,466 --> 00:40:05,094

1126
00:40:05,094 --> 00:40:06,260
JASON HIRSCHHORN: Oh, sorry.

1127
00:40:06,260 --> 00:40:07,870
This is just h.

1128
00:40:07,870 --> 00:40:09,585
Sorry, this is not clear.

1129
00:40:09,585 --> 00:40:10,920

1130
00:40:10,920 --> 00:40:12,412
>> STUDENT: So the top one--

1131
00:40:12,412 --> 00:40:14,120
JASON HIRSCHHORN: This
is a string, yeah.

1132
00:40:14,120 --> 00:40:15,430
So it's two characters, right?

1133
00:40:15,430 --> 00:40:16,360
String, hi.

1134
00:40:16,360 --> 00:40:19,030
But let's say I just
had a single character,

1135
00:40:19,030 --> 00:40:23,220
if I put two quotes around
just h, that's a string.

1136
00:40:23,220 --> 00:40:24,500
This is a string h.

1137
00:40:24,500 --> 00:40:25,660

1138
00:40:25,660 --> 00:40:26,940
Does that make sense?

1139
00:40:26,940 --> 00:40:28,705
So this is four bytes.

1140
00:40:28,705 --> 00:40:31,660
But let's say I got rid
of that an only put one.

1141
00:40:31,660 --> 00:40:33,940

1142
00:40:33,940 --> 00:40:34,830
One quote.

1143
00:40:34,830 --> 00:40:37,140
This is now a char, a char h.

1144
00:40:37,140 --> 00:40:38,440

1145
00:40:38,440 --> 00:40:42,410
So exact same thing,
different data type.

1146
00:40:42,410 --> 00:40:45,330
This is only one byte, whereas
the string was four bytes.

1147
00:40:45,330 --> 00:40:45,830
Yeah.

1148
00:40:45,830 --> 00:40:48,214

1149
00:40:48,214 --> 00:40:50,630
STUDENT: So if you were trying
to store a word like David,

1150
00:40:50,630 --> 00:40:54,436
you would want to use a string because
regardless of how long the string is,

1151
00:40:54,436 --> 00:40:57,760
it will only take four bytes
unless it's a long long

1152
00:40:57,760 --> 00:41:02,530
or a double, in which case-- so if it
extends beyond four characters, then

1153
00:41:02,530 --> 00:41:04,435
you want to make it into string.

1154
00:41:04,435 --> 00:41:05,810
Is that the general logic behind.

1155
00:41:05,810 --> 00:41:06,537

1156
00:41:06,537 --> 00:41:09,370
JASON HIRSCHHORN: If it extends
beyond one character, it's a string.

1157
00:41:09,370 --> 00:41:10,640

1158
00:41:10,640 --> 00:41:14,880
>> STUDENT: So there's no [INAUDIBLE]
to storing a four letter

1159
00:41:14,880 --> 00:41:18,370
word as four individual or three letter
word as three individual characters

1160
00:41:18,370 --> 00:41:22,050
because that will only be three bytes,
as opposed to the three part string.

1161
00:41:22,050 --> 00:41:23,611

1162
00:41:23,611 --> 00:41:25,110
JASON HIRSCHHORN: You could do that.

1163
00:41:25,110 --> 00:41:27,850

1164
00:41:27,850 --> 00:41:31,070
You could do that, but I don't
think that's really worthwhile,

1165
00:41:31,070 --> 00:41:32,570
because you're only saving one byte.

1166
00:41:32,570 --> 00:41:33,310
You know what I'm saying?

1167
00:41:33,310 --> 00:41:35,559
In the big scheme of things,
that won't really matter.

1168
00:41:35,559 --> 00:41:39,210
But for example, printf, if
you're printing f and you

1169
00:41:39,210 --> 00:41:43,430
have three chars you can print
that out-- let's say you C-A-T,

1170
00:41:43,430 --> 00:41:47,680
you can print out cat just by
doing one char one char one char,

1171
00:41:47,680 --> 00:41:49,980
or can you print out string cat.

1172
00:41:49,980 --> 00:41:51,140
It's the exact same thing.

1173
00:41:51,140 --> 00:41:52,870
So you could do it like that, but--

1174
00:41:52,870 --> 00:41:54,330
>> STUDENT: It's not going
to save you that much.

1175
00:41:54,330 --> 00:41:54,720
>> JASON HIRSCHHORN: Yeah.

1176
00:41:54,720 --> 00:41:57,125
The headache that it would
induce is not worth it.

1177
00:41:57,125 --> 00:41:59,049

1178
00:41:59,049 --> 00:42:00,020
Yeah?

1179
00:42:00,020 --> 00:42:02,920
>> STUDENT: For example,
you had the h with one

1180
00:42:02,920 --> 00:42:05,410
versus two, the single or double quotes.

1181
00:42:05,410 --> 00:42:08,760
Why would you want to save
a single letter as a string.

1182
00:42:08,760 --> 00:42:11,569
What purpose does that ever serve?

1183
00:42:11,569 --> 00:42:12,860
JASON HIRSCHHORN: I don't know.

1184
00:42:12,860 --> 00:42:14,568
I mean, it really
depends on the program.

1185
00:42:14,568 --> 00:42:16,060

1186
00:42:16,060 --> 00:42:20,800
For example, I think later on
you'll get into command line stuff.

1187
00:42:20,800 --> 00:42:24,770
So for example, instead of me
asking you for an integer-- sorry,

1188
00:42:24,770 --> 00:42:26,720
can I speak into you?

1189
00:42:26,720 --> 00:42:27,220
HANNAH: Yes.

1190
00:42:27,220 --> 00:42:30,660

1191
00:42:30,660 --> 00:42:32,450
>> JASON HIRSCHHORN: So
for example, instead

1192
00:42:32,450 --> 00:42:35,830
of me asking for something
with get end, which

1193
00:42:35,830 --> 00:42:38,854
I think you might have seen a lecture,
there might be a command line.

1194
00:42:38,854 --> 00:42:40,520
You just type it in at the command line.

1195
00:42:40,520 --> 00:42:46,690
It would be like -/hello4 or
something, or helloh h, whatever.

1196
00:42:46,690 --> 00:42:49,190
You do it at the command line
instead of being asked for it,

1197
00:42:49,190 --> 00:42:53,830
that command line is always a
string, whether it's a four or an h,

1198
00:42:53,830 --> 00:42:55,320
that is always a string.

1199
00:42:55,320 --> 00:42:59,130
So that's one example of when you might
have a singular letter or a singular

1200
00:42:59,130 --> 00:43:00,667
number represented as a string.

1201
00:43:00,667 --> 00:43:06,360

1202
00:43:06,360 --> 00:43:07,110
SHARON: All right.

1203
00:43:07,110 --> 00:43:08,230

1204
00:43:08,230 --> 00:43:09,855
And then here are some basic operators.

1205
00:43:09,855 --> 00:43:11,460

1206
00:43:11,460 --> 00:43:14,560
Hopefully you're familiar with
the first four just in general.

1207
00:43:14,560 --> 00:43:18,080
So there's adding, subtracting,
multiplying, and dividing,

1208
00:43:18,080 --> 00:43:23,535
and make sure you use
the right keystrokes.

1209
00:43:23,535 --> 00:43:25,260

1210
00:43:25,260 --> 00:43:29,640
>> And then there's also modulo, which some
of you might not be very familiar with.

1211
00:43:29,640 --> 00:43:34,900
And what modulo does is that
if we take this example 4 % 2,

1212
00:43:34,900 --> 00:43:37,990
it takes the remainder of
what that does in division.

1213
00:43:37,990 --> 00:43:41,670
So 4 divided by 2 is 2,
and there's no remainder.

1214
00:43:41,670 --> 00:43:47,880
4 divide by 3 is 1 and
1/3, and so remainder 1.

1215
00:43:47,880 --> 00:43:49,320
So it computes to one.

1216
00:43:49,320 --> 00:43:56,960
And then 4 % 5 is the fraction
4/5, and the remainder is 4.

1217
00:43:56,960 --> 00:43:58,580
Does that make sense?

1218
00:43:58,580 --> 00:43:59,580
OK, cool.

1219
00:43:59,580 --> 00:44:01,080

1220
00:44:01,080 --> 00:44:03,110
And we follow PEMDAS here too.

1221
00:44:03,110 --> 00:44:06,240

1222
00:44:06,240 --> 00:44:07,740
>> So some Boolean expressions.

1223
00:44:07,740 --> 00:44:08,920

1224
00:44:08,920 --> 00:44:16,890
So you guys have seen equals equals
to compare, say, two numbers.

1225
00:44:16,890 --> 00:44:20,440
So if 5 equals equals 5,
that computes to true.

1226
00:44:20,440 --> 00:44:22,190
Make sure you have only one equals sign.

1227
00:44:22,190 --> 00:44:23,530

1228
00:44:23,530 --> 00:44:27,030
For not equals, it's
bang or exclamation.

1229
00:44:27,030 --> 00:44:28,960
>> HANNAH: Two equal signs
when you do equality.

1230
00:44:28,960 --> 00:44:29,290
>> SHARON: Oh, yeah.

1231
00:44:29,290 --> 00:44:30,998
Make sure you don't
have one equals sign.

1232
00:44:30,998 --> 00:44:32,320

1233
00:44:32,320 --> 00:44:35,745
And then for not equals,
it's bang equals.

1234
00:44:35,745 --> 00:44:37,000

1235
00:44:37,000 --> 00:44:40,540
And then you can look through
for less than, greater than.

1236
00:44:40,540 --> 00:44:44,300
And then we have logical and
and logical or right here.

1237
00:44:44,300 --> 00:44:47,190
And what that does is, if
you remember in Scratch

1238
00:44:47,190 --> 00:44:51,000
when you had that block
that said and, and then you

1239
00:44:51,000 --> 00:44:54,860
could fit two different pieces
there, that's what this and does.

1240
00:44:54,860 --> 00:44:56,450
And make sure you do two ampersands.

1241
00:44:56,450 --> 00:44:57,590

1242
00:44:57,590 --> 00:45:04,110
And this key you can find towards the
right, right under your Delete button.

1243
00:45:04,110 --> 00:45:07,820

1244
00:45:07,820 --> 00:45:08,907
Question?

1245
00:45:08,907 --> 00:45:10,398
>> STUDENT: What was the [INAUDIBLE]?

1246
00:45:10,398 --> 00:45:16,900

1247
00:45:16,900 --> 00:45:20,400
>> SHARON: OK, so if you only do
one, you're comparing bits.

1248
00:45:20,400 --> 00:45:22,040

1249
00:45:22,040 --> 00:45:26,400
So if you remember what bits
are, they're 0's and 1's, and so

1250
00:45:26,400 --> 00:45:27,740
that's comparing something else.

1251
00:45:27,740 --> 00:45:29,440
So we're going to focus on this for now.

1252
00:45:29,440 --> 00:45:31,856
>> JASON HIRSCHHORN: So one equals
is like assignment, right?

1253
00:45:31,856 --> 00:45:33,170
So like int x equals 4.

1254
00:45:33,170 --> 00:45:38,080
You're saying that variable x equals 4.

1255
00:45:38,080 --> 00:45:42,910
So 1 equals is assignment,
but the ands and the pipes

1256
00:45:42,910 --> 00:45:45,820
or the bars, just like Sharon
said, they're bitwise operators.

1257
00:45:45,820 --> 00:45:47,620
You don't need to worry about that.

1258
00:45:47,620 --> 00:45:49,120

1259
00:45:49,120 --> 00:45:51,620
>> STUDENT: When do you use logical
and and logical or again?

1260
00:45:51,620 --> 00:45:54,620
I just forgot when you do that.

1261
00:45:54,620 --> 00:45:57,510
>> HANNAH: Sure, so if you ever want
to check if two things are true,

1262
00:45:57,510 --> 00:46:01,550
for example, let's say I want to check
that a number is between 5 and 15,

1263
00:46:01,550 --> 00:46:04,660
I would say make sure that
the number is greater than 5.

1264
00:46:04,660 --> 00:46:09,430
So let's say if x is greater
than 5 and less than 15.

1265
00:46:09,430 --> 00:46:12,630
So in order for that whole
statement to evaluate to true,

1266
00:46:12,630 --> 00:46:16,290
you need both of the kind of sub
statements to evaluate the true.

1267
00:46:16,290 --> 00:46:18,481
With or you only need
one of the two or both.

1268
00:46:18,481 --> 00:46:19,564
STUDENT: Great, thank you.

1269
00:46:19,564 --> 00:46:20,820

1270
00:46:20,820 --> 00:46:24,980
>> SHARON: And also in Scratch, I'm
sure in a lot of your projects

1271
00:46:24,980 --> 00:46:31,059
you had if touching the edge or if
touching another sprite then bounce

1272
00:46:31,059 --> 00:46:31,600
or something.

1273
00:46:31,600 --> 00:46:34,362

1274
00:46:34,362 --> 00:46:37,070
HANNAH: All right, so why do we
care about all of these Booleans?

1275
00:46:37,070 --> 00:46:40,600
We have these structures that you've
seen in Scratch called conditionals.

1276
00:46:40,600 --> 00:46:44,830
And conditionals are anything of the
form if some condition or some Boolean

1277
00:46:44,830 --> 00:46:48,970
is true, then do the code
between these curly braces.

1278
00:46:48,970 --> 00:46:51,220
So you can see on the right
here is the Scratch block.

1279
00:46:51,220 --> 00:46:55,132
You have this if then, and anything
that goes into that little shape that

1280
00:46:55,132 --> 00:46:56,840
looks like this-- i
don't know what you'd

1281
00:46:56,840 --> 00:46:59,960
call that-- that's going to
be the Boolean or condition.

1282
00:46:59,960 --> 00:47:01,880
>> So again, a Boolean or
condition is anything

1283
00:47:01,880 --> 00:47:04,500
that either evaluate to true or false.

1284
00:47:04,500 --> 00:47:06,150
And again, you can combine Booleans.

1285
00:47:06,150 --> 00:47:10,740
You can have, again, x is greater
than 5 and x is less than 15.

1286
00:47:10,740 --> 00:47:13,610
Or you can just have one
of those x is less than 5.

1287
00:47:13,610 --> 00:47:16,850
>> OK, so in C It's on the left.

1288
00:47:16,850 --> 00:47:18,270
It's just the keyword if.

1289
00:47:18,270 --> 00:47:20,750
In parentheses, the
condition or the Boolean.

1290
00:47:20,750 --> 00:47:23,590
And then the code in between
those two curly braces

1291
00:47:23,590 --> 00:47:28,746
will only execute, will only run if
that condition or that Boolean is true.

1292
00:47:28,746 --> 00:47:30,385
Does that make sense?

1293
00:47:30,385 --> 00:47:30,885
Awesome.

1294
00:47:30,885 --> 00:47:31,570
OK.

1295
00:47:31,570 --> 00:47:33,278
And then as you may
have seen in Scratch,

1296
00:47:33,278 --> 00:47:35,830
we can also add on an
else, which is basically

1297
00:47:35,830 --> 00:47:38,820
anything between the
curly braces under else

1298
00:47:38,820 --> 00:47:41,430
will only execute if
the condition is false.

1299
00:47:41,430 --> 00:47:42,610

1300
00:47:42,610 --> 00:47:43,600
Make sense?

1301
00:47:43,600 --> 00:47:44,840
Any questions on these two?

1302
00:47:44,840 --> 00:47:45,905

1303
00:47:45,905 --> 00:47:46,405
Awesome.

1304
00:47:46,405 --> 00:47:48,430

1305
00:47:48,430 --> 00:47:49,125
>> Cool.

1306
00:47:49,125 --> 00:47:50,650
So here's a quick example.

1307
00:47:50,650 --> 00:47:54,410
Let's say we want to
determine, based on the time,

1308
00:47:54,410 --> 00:47:56,760
whether we should say good
morning or good evening.

1309
00:47:56,760 --> 00:48:00,480
I'll say if it's before 12:00 noon,
we're going to say good morning,

1310
00:48:00,480 --> 00:48:02,940
otherwise we're going
to say good evening.

1311
00:48:02,940 --> 00:48:07,180
And when I said that otherwise,
that's equivalent in C to this else.

1312
00:48:07,180 --> 00:48:10,580
So we're going to check if the
military time is less than 12:00,

1313
00:48:10,580 --> 00:48:12,060
say good morning.

1314
00:48:12,060 --> 00:48:14,025
Otherwise say good evening.

1315
00:48:14,025 --> 00:48:17,500
>> STUDENT: So we'd actually get that input
for military time with the get string.

1316
00:48:17,500 --> 00:48:18,097

1317
00:48:18,097 --> 00:48:18,680
HANNAH: Right.

1318
00:48:18,680 --> 00:48:22,110
Did Somewhere else we'd actually
have to provide that information.

1319
00:48:22,110 --> 00:48:23,700
Right here it has no value.

1320
00:48:23,700 --> 00:48:25,510
We never even declared it.

1321
00:48:25,510 --> 00:48:28,630
I assume that somewhere above
this program I declared the time,

1322
00:48:28,630 --> 00:48:32,090
or asked the time, or--
anything else with this example?

1323
00:48:32,090 --> 00:48:33,560

1324
00:48:33,560 --> 00:48:34,060
Awesome.

1325
00:48:34,060 --> 00:48:35,750

1326
00:48:35,750 --> 00:48:40,490
>> OK, now we have in addition
to that simple if else format,

1327
00:48:40,490 --> 00:48:42,899
we have two other different structures.

1328
00:48:42,899 --> 00:48:44,940
So first we have the switch
statement, and here's

1329
00:48:44,940 --> 00:48:46,564
the general form of a switch statement.

1330
00:48:46,564 --> 00:48:49,450

1331
00:48:49,450 --> 00:48:53,110
You have the keyword switch the
same way you have the keyword if.

1332
00:48:53,110 --> 00:48:56,250
And then an input, in this case n.

1333
00:48:56,250 --> 00:48:58,410
So this can only work with integers.

1334
00:48:58,410 --> 00:49:02,270
So that input n has
to be an integer, OK?

1335
00:49:02,270 --> 00:49:04,950
And we're going to
follow one of these cases

1336
00:49:04,950 --> 00:49:07,430
depending on what that value n is.

1337
00:49:07,430 --> 00:49:12,170
>> So in this case, you first compare
is n equal to constant one,

1338
00:49:12,170 --> 00:49:15,844
if it is, do everything
kind of indented over here.

1339
00:49:15,844 --> 00:49:17,510
I can point to it because I'm too short.

1340
00:49:17,510 --> 00:49:19,400

1341
00:49:19,400 --> 00:49:23,210
If it's not equal to constant one
and is instead equal to constant two,

1342
00:49:23,210 --> 00:49:27,060
we're going to follow that second block,
and we can do this for as many times

1343
00:49:27,060 --> 00:49:32,890
as we want, and then that default is if
it didn't match any of the above cases,

1344
00:49:32,890 --> 00:49:33,820
execute that code.

1345
00:49:33,820 --> 00:49:35,759

1346
00:49:35,759 --> 00:49:36,550
Any questions here?

1347
00:49:36,550 --> 00:49:38,133
This one is a little more complicated.

1348
00:49:38,133 --> 00:49:38,633

1349
00:49:38,633 --> 00:49:39,395
Yeah?

1350
00:49:39,395 --> 00:49:41,820
>> STUDENT: Break signifying what?

1351
00:49:41,820 --> 00:49:45,560
>> HANNAH: Sure, so once we enter
that block, if we find, let's say,

1352
00:49:45,560 --> 00:49:50,940
our n is in fact equal to constant one,
we enter that block after the colon.

1353
00:49:50,940 --> 00:49:54,840
We do whatever is on
that line of commenting,

1354
00:49:54,840 --> 00:49:58,182
and then we break, meaning we get out
of this switch statement entirely.

1355
00:49:58,182 --> 00:49:58,682
STUDENT: OK.

1356
00:49:58,682 --> 00:49:59,830

1357
00:49:59,830 --> 00:50:00,562
>> HANNAH: Mm-hm?

1358
00:50:00,562 --> 00:50:03,311
>> STUDENT: Is the indentation
necessary, or do you need [INAUDIBLE]?

1359
00:50:03,311 --> 00:50:03,959

1360
00:50:03,959 --> 00:50:04,500
HANNAH: Sure.

1361
00:50:04,500 --> 00:50:07,640
So, as always, indentation
is not strictly necessary.

1362
00:50:07,640 --> 00:50:09,930
The computer doesn't
care whether you indent.

1363
00:50:09,930 --> 00:50:12,630
We, as people who are
reading your code, do care.

1364
00:50:12,630 --> 00:50:15,100
So it's a lot easier to
look up at the screen

1365
00:50:15,100 --> 00:50:19,707
and see, oh, I know exactly what
happens when n is equal to constant one.

1366
00:50:19,707 --> 00:50:22,290
If I had random indents, I
wouldn't be able to tell so easily.

1367
00:50:22,290 --> 00:50:23,276
Yeah?

1368
00:50:23,276 --> 00:50:27,466
>> STUDENT: So if wanted a user to
choose one of the options that

1369
00:50:27,466 --> 00:50:31,657
we have on the list, would
we use, I guess, [INAUDIBLE],

1370
00:50:31,657 --> 00:50:35,108
but get an integer from
them and put that into n?

1371
00:50:35,108 --> 00:50:36,844

1372
00:50:36,844 --> 00:50:37,760
HANNAH: Exactly right.

1373
00:50:37,760 --> 00:50:40,330
So let's say we wanted
to check what integer.

1374
00:50:40,330 --> 00:50:45,380
We said oh, enter an integer
between 0 and 5, let's say.

1375
00:50:45,380 --> 00:50:47,790
We could ask for that
n, ask for that value,

1376
00:50:47,790 --> 00:50:50,000
and then have each of those cases.

1377
00:50:50,000 --> 00:50:53,230
And again, this is something we could
very easily do with if statements,

1378
00:50:53,230 --> 00:50:53,730
right?

1379
00:50:53,730 --> 00:50:56,920
We could have if equal to case
one, if equal to case two,

1380
00:50:56,920 --> 00:50:58,910
if equal to case three,
so on and so forth.

1381
00:50:58,910 --> 00:51:01,680
This is a little bit faster
and a little cleaner.

1382
00:51:01,680 --> 00:51:04,201
It's kind of just a nice structure now.

1383
00:51:04,201 --> 00:51:05,450
STUDENT: Faster as in writing?

1384
00:51:05,450 --> 00:51:06,830
Or does it run the
computer a little faster?

1385
00:51:06,830 --> 00:51:08,246
>> HANNAH: It's runs a little faster.

1386
00:51:08,246 --> 00:51:09,214

1387
00:51:09,214 --> 00:51:09,714
Yeah?

1388
00:51:09,714 --> 00:51:13,490
>> STUDENT: So the double
dash is just comment or--

1389
00:51:13,490 --> 00:51:14,700
>> HANNAH: Oh, I'm so sorry.

1390
00:51:14,700 --> 00:51:15,700
I didn't point that out.

1391
00:51:15,700 --> 00:51:17,790
OK, if you have that //, is a comment.

1392
00:51:17,790 --> 00:51:19,250

1393
00:51:19,250 --> 00:51:20,770
Just // is a comment.

1394
00:51:20,770 --> 00:51:23,030
So any time the computer
sees that, it's going

1395
00:51:23,030 --> 00:51:25,760
to say OK, anything that follows
this, I'm just going to ignore.

1396
00:51:25,760 --> 00:51:27,310
I'm going to pretend you
never even wrote that.

1397
00:51:27,310 --> 00:51:28,850
>> STUDENT: So this [INAUDIBLE].

1398
00:51:28,850 --> 00:51:30,650
>> HANNAH: This does absolutely nothing.

1399
00:51:30,650 --> 00:51:37,360
But if I wrote something like on the
first comment I wrote instead printf

1400
00:51:37,360 --> 00:51:41,640
say congratulations you entered
constant one, that would be something.

1401
00:51:41,640 --> 00:51:42,140
Yeah?

1402
00:51:42,140 --> 00:51:44,515
>> STUDENT: So in real life, the
case would just simply be a number

1403
00:51:44,515 --> 00:51:46,420
and then [INAUDIBLE]
would be another integer.

1404
00:51:46,420 --> 00:51:46,763
>> HANNAH: Exactly.

1405
00:51:46,763 --> 00:51:48,550
>> STUDENT: And do you need the ellipses?

1406
00:51:48,550 --> 00:51:48,805
>> HANNAH: Sorry?

1407
00:51:48,805 --> 00:51:49,550
>> STUDENT: Do you need that?

1408
00:51:49,550 --> 00:51:50,010
>> HANNAH: Oh, no.

1409
00:51:50,010 --> 00:51:50,560
I'm sorry.

1410
00:51:50,560 --> 00:51:53,684
That was just to indicate that you can
go on for as many cases as you want.

1411
00:51:53,684 --> 00:51:56,950
Let's do a concrete example that
might make things a little more clear.

1412
00:51:56,950 --> 00:52:01,440
OK, so let's say I say,
OK, give me an integer n

1413
00:52:01,440 --> 00:52:05,010
that represents a class number,
specifically a computer science class

1414
00:52:05,010 --> 00:52:05,720
number.

1415
00:52:05,720 --> 00:52:07,950
So if you give me 50,
I'm going to say great.

1416
00:52:07,950 --> 00:52:12,020
CS50 is an introduction to computer
science, and then I'm going to break.

1417
00:52:12,020 --> 00:52:14,810
So that means I jump out of
this whole switch statement,

1418
00:52:14,810 --> 00:52:17,020
so now I'm done running the code, OK?

1419
00:52:17,020 --> 00:52:21,410
>> If you gave me instead 51, I'd
print the second statement.

1420
00:52:21,410 --> 00:52:24,720
And then if you gave me some
number that wasn't 50 or 51,

1421
00:52:24,720 --> 00:52:27,133
I'm going to say sorry, I'm
not familiar with that class.

1422
00:52:27,133 --> 00:52:28,019
Yeah?

1423
00:52:28,019 --> 00:52:29,350
>> STUDENT: You don't have break.

1424
00:52:29,350 --> 00:52:30,400
>> HANNAH: I'm sorry, I don't have break?

1425
00:52:30,400 --> 00:52:31,510
>> STUDENT: What if.

1426
00:52:31,510 --> 00:52:32,450
>> HANNAH: Oh, what if
you don't have break?

1427
00:52:32,450 --> 00:52:33,450
Excellent question.

1428
00:52:33,450 --> 00:52:37,890
So what would happen is you would go in,
and you would check am I equal to 50?

1429
00:52:37,890 --> 00:52:42,064
And let's say, yes, you were equal
to 50, you'd print the statement.

1430
00:52:42,064 --> 00:52:45,105
And then you would continue executing,
so you would say am I equal to 51?

1431
00:52:45,105 --> 00:52:46,500

1432
00:52:46,500 --> 00:52:49,763
And you would go on and go
through every case like that?

1433
00:52:49,763 --> 00:52:50,262
Yes?

1434
00:52:50,262 --> 00:52:52,894
>> STUDENT: Is the default line
analogous to saying else?

1435
00:52:52,894 --> 00:52:53,560
HANNAH: Exactly.

1436
00:52:53,560 --> 00:52:54,060
Very good.

1437
00:52:54,060 --> 00:52:56,140
It's like the kind of catch all.

1438
00:52:56,140 --> 00:53:00,574
>> STUDENT: So if you didn't have break
and then one of the case statements

1439
00:53:00,574 --> 00:53:03,843
was true, and then it
said increase n by 1,

1440
00:53:03,843 --> 00:53:09,210
then it would automatically
make the next one.

1441
00:53:09,210 --> 00:53:11,657
It would check case 51, and
then display that as well?

1442
00:53:11,657 --> 00:53:13,240
HANNAH: Yeah, I think that would work.

1443
00:53:13,240 --> 00:53:15,740
So you could kind of get messy, so
a break is a good thing to have.

1444
00:53:15,740 --> 00:53:16,240
Yeah?

1445
00:53:16,240 --> 00:53:18,557
STUDENT: Without break
would it do the default?

1446
00:53:18,557 --> 00:53:19,890
HANNAH: That is a good question.

1447
00:53:19,890 --> 00:53:20,590
JASON HIRSCHHORN: I think it just runs.

1448
00:53:20,590 --> 00:53:23,975
So if you don't have break-- so
let's say I did 50 and it checked 50,

1449
00:53:23,975 --> 00:53:25,306
and it would print that out.

1450
00:53:25,306 --> 00:53:27,430
Print out CS50 as introduction
to computer science.

1451
00:53:27,430 --> 00:53:30,549
You don't have break, it should go
and keep going until it hits a break.

1452
00:53:30,549 --> 00:53:32,590
So if there's no break,
it's going to keep going.

1453
00:53:32,590 --> 00:53:34,190
It's going to print everything else out.

1454
00:53:34,190 --> 00:53:35,695
>> HANNAH: So I guess that would
be including the default.

1455
00:53:35,695 --> 00:53:36,020
>> JASON HIRSCHHORN: Yeah.

1456
00:53:36,020 --> 00:53:36,720
>> HANNAH: Good question.

1457
00:53:36,720 --> 00:53:37,220
Yeah?

1458
00:53:37,220 --> 00:53:39,070
STUDENT: Is case considered a function?

1459
00:53:39,070 --> 00:53:39,820
HANNAH: I'm sorry?

1460
00:53:39,820 --> 00:53:41,570
STUDENT: Is case considered a function?

1461
00:53:41,570 --> 00:53:43,153
HANNAH: Is case considered a function.

1462
00:53:43,153 --> 00:53:45,520

1463
00:53:45,520 --> 00:53:46,840
I would hesitate to say that.

1464
00:53:46,840 --> 00:53:52,000
>> JASON HIRSCHHORN: So normally
when you see functions

1465
00:53:52,000 --> 00:53:54,370
they'll be in curly braces.

1466
00:53:54,370 --> 00:53:57,840
So for example, when you look
at your code, for example, main.

1467
00:53:57,840 --> 00:54:01,450
It was main open paren,
then void, close paren.

1468
00:54:01,450 --> 00:54:05,415
Functions-- they're basically
always you'll see parentheses.

1469
00:54:05,415 --> 00:54:07,290
So case if case doesn't
have any parentheses,

1470
00:54:07,290 --> 00:54:09,556
that's your clue that
that's not a function.

1471
00:54:09,556 --> 00:54:10,984
But it's not.

1472
00:54:10,984 --> 00:54:12,388

1473
00:54:12,388 --> 00:54:12,888
Yeah?

1474
00:54:12,888 --> 00:54:15,280
>> STUDENT: So then does that
make switch a function?

1475
00:54:15,280 --> 00:54:16,150
>> HANNAH: Does that makes
switch a function.

1476
00:54:16,150 --> 00:54:18,149
>> STUDENT: In the sense
that you put something in,

1477
00:54:18,149 --> 00:54:19,399
it gives you one of the cases.

1478
00:54:19,399 --> 00:54:21,399
JASON HIRSCHHORN: I
wouldn't call it a function.

1479
00:54:21,399 --> 00:54:23,120
Not everything with
parens is a function.

1480
00:54:23,120 --> 00:54:25,629

1481
00:54:25,629 --> 00:54:27,420
I mean that's a clue
that it is a function.

1482
00:54:27,420 --> 00:54:30,990
I wouldn't say switch is a
function because it's not really

1483
00:54:30,990 --> 00:54:32,207
returning anything.

1484
00:54:32,207 --> 00:54:33,290
You'll get into that more.

1485
00:54:33,290 --> 00:54:34,380

1486
00:54:34,380 --> 00:54:36,476
>> HANNAH: Yeah, just think
of it as an if structure.

1487
00:54:36,476 --> 00:54:38,392
STUDENT: Can you nest
this in an if structure?

1488
00:54:38,392 --> 00:54:40,197

1489
00:54:40,197 --> 00:54:42,030
HANNAH: Yeah, you nest
pretty much anything.

1490
00:54:42,030 --> 00:54:43,170

1491
00:54:43,170 --> 00:54:46,138
>> STUDENT: Barry said the quotes
are sort of like the same as else.

1492
00:54:46,138 --> 00:54:48,428
So can you replace the quotes with else?

1493
00:54:48,428 --> 00:54:49,750

1494
00:54:49,750 --> 00:54:52,510
>> HANNAH: Not in this particular
structure because the switch

1495
00:54:52,510 --> 00:54:55,250
statement is expecting the word default.

1496
00:54:55,250 --> 00:54:58,427
The computer knows that default
means something special, that

1497
00:54:58,427 --> 00:54:59,260
means the catch all.

1498
00:54:59,260 --> 00:55:00,344

1499
00:55:00,344 --> 00:55:01,260
Anything else on this.

1500
00:55:01,260 --> 00:55:02,750
We have one more to get through.

1501
00:55:02,750 --> 00:55:03,654
Yeah?

1502
00:55:03,654 --> 00:55:04,529
>> STUDENT: [INAUDIBLE].

1503
00:55:04,529 --> 00:55:06,246

1504
00:55:06,246 --> 00:55:08,620
HANNAH: Difference between
using a semicolon and a colon.

1505
00:55:08,620 --> 00:55:13,090
So a semicolon is always to tell the
computer I am done with this line.

1506
00:55:13,090 --> 00:55:14,440
You can go ahead and execute it.

1507
00:55:14,440 --> 00:55:15,940
This is a complete line.

1508
00:55:15,940 --> 00:55:20,270
A colon is going to, in this case,
bring you into a particular block.

1509
00:55:20,270 --> 00:55:21,510

1510
00:55:21,510 --> 00:55:23,790
So semicolons are
always use to end lines.

1511
00:55:23,790 --> 00:55:26,603
Colons are used for a
variety of other cases.

1512
00:55:26,603 --> 00:55:30,547
>> STUDENT: Is this equivalent to
just saying if n equals 50, then

1513
00:55:30,547 --> 00:55:31,443
blah blah blah.

1514
00:55:31,443 --> 00:55:32,026
HANNAH: Mm-hm.

1515
00:55:32,026 --> 00:55:33,998
STUDENT: It's just the same [INAUDIBLE].

1516
00:55:33,998 --> 00:55:34,804

1517
00:55:34,804 --> 00:55:35,470
HANNAH: Exactly.

1518
00:55:35,470 --> 00:55:37,870
And we said it runs a little bit faster.

1519
00:55:37,870 --> 00:55:41,510
If we did not have the break,
it would be like if, if, if.

1520
00:55:41,510 --> 00:55:45,406
If we do have the break, it's
like if else if else if else if.

1521
00:55:45,406 --> 00:55:47,340

1522
00:55:47,340 --> 00:55:47,840
Cool?

1523
00:55:47,840 --> 00:55:50,298
>> JASON HIRSCHHORN: So when
coding, you can just use if else,

1524
00:55:50,298 --> 00:55:54,000
but I think last year on the quiz we
had them write a switch statement,

1525
00:55:54,000 --> 00:55:54,700
so just in case.

1526
00:55:54,700 --> 00:55:56,339

1527
00:55:56,339 --> 00:55:57,880
HANNAH: But definitely nothing wrong.

1528
00:55:57,880 --> 00:56:00,820
We're not expecting you to worry
about performance crazy things.

1529
00:56:00,820 --> 00:56:02,780
Just if else is totally fine.

1530
00:56:02,780 --> 00:56:04,530
These are just good
things to be aware of.

1531
00:56:04,530 --> 00:56:07,770
>> And here's our last one that kind of
falls under this conditional category.

1532
00:56:07,770 --> 00:56:08,970

1533
00:56:08,970 --> 00:56:12,810
We have something of the
general form condition ?,

1534
00:56:12,810 --> 00:56:16,350
and then a little piece of code that
happens if the condition is true.

1535
00:56:16,350 --> 00:56:18,780
And then colon, a little
piece of code that

1536
00:56:18,780 --> 00:56:21,270
executes if the condition
is false, semicolon.

1537
00:56:21,270 --> 00:56:22,504
We're done with that line.

1538
00:56:22,504 --> 00:56:24,170
So syntactically it's a little bit ugly.

1539
00:56:24,170 --> 00:56:26,850
We're going to go through an
example I think that's most clear.

1540
00:56:26,850 --> 00:56:31,420
So we want to assign
the string professor

1541
00:56:31,420 --> 00:56:35,900
to one of these two values, either
David Malan or not David Malan, OK?

1542
00:56:35,900 --> 00:56:38,740
So you should be familiar
with the string, professor =.

1543
00:56:38,740 --> 00:56:41,770
We're going to assign a string
to the variable called professor.

1544
00:56:41,770 --> 00:56:43,440

1545
00:56:43,440 --> 00:56:46,360
>> Now we want to check a
particular condition.

1546
00:56:46,360 --> 00:56:50,700
In this case, our condition
is class_num = = 50.

1547
00:56:50,700 --> 00:56:53,080
And now might be a
good time to point out

1548
00:56:53,080 --> 00:56:56,500
when we have string professor
=, that's one equals sign.

1549
00:56:56,500 --> 00:56:57,870
That's assignment.

1550
00:56:57,870 --> 00:57:01,360
Whereas in class_num = =
50, that's two equal signs.

1551
00:57:01,360 --> 00:57:03,050
That's a quality check.

1552
00:57:03,050 --> 00:57:06,000
So we're going to say is the
class number equal to 50?

1553
00:57:06,000 --> 00:57:10,060
If so, assign Professor David Malan.

1554
00:57:10,060 --> 00:57:13,710
If not, assign professor
to not David Malan.

1555
00:57:13,710 --> 00:57:15,320

1556
00:57:15,320 --> 00:57:16,327
Any questions there?

1557
00:57:16,327 --> 00:57:18,410
Again, this is just something
that's good to know.

1558
00:57:18,410 --> 00:57:20,230
You could do this with if else.

1559
00:57:20,230 --> 00:57:22,550
A good practice problem
might be to, when

1560
00:57:22,550 --> 00:57:27,830
you go home, right the same exact
conditional in an if else form,

1561
00:57:27,830 --> 00:57:28,830
because you can do that.

1562
00:57:28,830 --> 00:57:29,950

1563
00:57:29,950 --> 00:57:30,785
Any questions here?

1564
00:57:30,785 --> 00:57:31,829

1565
00:57:31,829 --> 00:57:33,870
All right, I think we're
going to go on to loops.

1566
00:57:33,870 --> 00:57:34,881

1567
00:57:34,881 --> 00:57:35,380
Awesome.

1568
00:57:35,380 --> 00:57:36,780

1569
00:57:36,780 --> 00:57:38,730
>> SHARON: OK, let's talk
about while loops.

1570
00:57:38,730 --> 00:57:49,995
So first on the left you see here--
OK that says while, while (condition).

1571
00:57:49,995 --> 00:57:51,040

1572
00:57:51,040 --> 00:57:53,142
And then you do this--
can we change this?

1573
00:57:53,142 --> 00:57:54,433
>> JASON HIRSCHHORN: It's cut off.

1574
00:57:54,433 --> 00:57:55,420

1575
00:57:55,420 --> 00:57:58,010
>> SHARON: OK, and then there
are also curly braces.

1576
00:57:58,010 --> 00:58:01,680
So pretend that curly
braces are there above

1577
00:58:01,680 --> 00:58:04,070
and below the do this again and again.

1578
00:58:04,070 --> 00:58:10,930
So if the condition in those
parentheses evaluates to true,

1579
00:58:10,930 --> 00:58:15,150
then you should keep doing
whatever is in the while loop.

1580
00:58:15,150 --> 00:58:19,610
>> So for example, we could
do a practice problem.

1581
00:58:19,610 --> 00:58:20,760

1582
00:58:20,760 --> 00:58:23,750
I'm wearing two earrings
right now, so let's say

1583
00:58:23,750 --> 00:58:27,580
if I'm wearing at least one
hearing, clap your hands.

1584
00:58:27,580 --> 00:58:30,060
So if we're going to go
through this, we're going--

1585
00:58:30,060 --> 00:58:30,790
>> [CLAPPING]

1586
00:58:30,790 --> 00:58:31,930
>> Right?

1587
00:58:31,930 --> 00:58:36,710
And I'm wearing one, and-- OK.

1588
00:58:36,710 --> 00:58:37,300
Yeah.

1589
00:58:37,300 --> 00:58:39,850
I'm not wearing earrings
anymore, so no more.

1590
00:58:39,850 --> 00:58:41,980
OK, so then that's when you would stop.

1591
00:58:41,980 --> 00:58:45,980
And this you could say is
equivalent to almost variables.

1592
00:58:45,980 --> 00:58:50,190
Let's say you have a
variable number of earrings.

1593
00:58:50,190 --> 00:58:51,660

1594
00:58:51,660 --> 00:59:00,940
So while number of earrings is greater
than or equal to 1, clap hands.

1595
00:59:00,940 --> 00:59:08,310
And then after clap
hands, decrement earrings.

1596
00:59:08,310 --> 00:59:11,060
Do like earrings minus 1.

1597
00:59:11,060 --> 00:59:15,205
So decrement the number of earrings, and
then you will go through the while loop

1598
00:59:15,205 --> 00:59:16,300
twice.

1599
00:59:16,300 --> 00:59:24,780
>> And if the condition is always
true-- so if, let's say, 2 = = 2,

1600
00:59:24,780 --> 00:59:28,670
and 2 is always equal to 2, right?

1601
00:59:28,670 --> 00:59:30,780
Then you would always
do something in there,

1602
00:59:30,780 --> 00:59:35,500
and that's equivalent to almost the
forever loop that we had in Scratch.

1603
00:59:35,500 --> 00:59:36,865

1604
00:59:36,865 --> 00:59:37,364
Yes?

1605
00:59:37,364 --> 00:59:41,100
>> STUDENT: Are the two sides just
different ways of writing a while loop?

1606
00:59:41,100 --> 00:59:43,100
>> SHARON: So we're focused
on this one first.

1607
00:59:43,100 --> 00:59:45,520
And then so let's compare
it with a do while loop.

1608
00:59:45,520 --> 00:59:47,460
So they're slightly different.

1609
00:59:47,460 --> 00:59:54,120
OK, so let's say the condition is still
while I'm wearing at least one earring,

1610
00:59:54,120 --> 00:59:56,410
and I'm not wearing
any earrings right now.

1611
00:59:56,410 --> 01:00:01,860
And let's say do and still clap while
I'm wearing at least one earring.

1612
01:00:01,860 --> 01:00:02,850
What should happen?

1613
01:00:02,850 --> 01:00:04,236
>> [CLAPS]

1614
01:00:04,236 --> 01:00:06,210
>> Uh oh, guys.

1615
01:00:06,210 --> 01:00:11,820
OK, so you're supposed to clap
once because basically you

1616
01:00:11,820 --> 01:00:13,510
go through the first part of the code.

1617
01:00:13,510 --> 01:00:18,630
You do it no matter what, and
then you see the while condition,

1618
01:00:18,630 --> 01:00:22,640
and you go back into
that loop if it's true.

1619
01:00:22,640 --> 01:00:23,969

1620
01:00:23,969 --> 01:00:24,885
Does that makes sense?

1621
01:00:24,885 --> 01:00:26,593
>> STUDENT: You always
do it the first time.

1622
01:00:26,593 --> 01:00:29,810
SHARON: You always do it the
first time regardless of whether

1623
01:00:29,810 --> 01:00:31,659
or not that condition is true or not.

1624
01:00:31,659 --> 01:00:33,950
JASON HIRSCHHORN: When do
you think you could use this?

1625
01:00:33,950 --> 01:00:35,480
When does it make sense to use this?

1626
01:00:35,480 --> 01:00:36,839

1627
01:00:36,839 --> 01:00:37,380
HANNAH: Yeah?

1628
01:00:37,380 --> 01:00:38,255
STUDENT: [INAUDIBLE].

1629
01:00:38,255 --> 01:00:40,080

1630
01:00:40,080 --> 01:00:41,080
JASON HIRSCHHORN: Right.

1631
01:00:41,080 --> 01:00:41,575
HANNAH: Very good.

1632
01:00:41,575 --> 01:00:43,408
JASON HIRSCHHORN: So
when you prompt a user,

1633
01:00:43,408 --> 01:00:45,947
you're going to always want
to prompt a user one time.

1634
01:00:45,947 --> 01:00:48,280
You're always going to want
to prompt the user one time.

1635
01:00:48,280 --> 01:00:50,103
So instead of putting
in a while loop, you

1636
01:00:50,103 --> 01:00:52,820
put in do while loop, because you're
always going to do it one time.

1637
01:00:52,820 --> 01:00:54,730
If they give you the
correct answer, you're done.

1638
01:00:54,730 --> 01:00:56,355
If they don't, then you re-prompt them.

1639
01:00:56,355 --> 01:01:02,080

1640
01:01:02,080 --> 01:01:03,360
>> SHARON: All right, for loops.

1641
01:01:03,360 --> 01:01:05,830

1642
01:01:05,830 --> 01:01:08,590
So in Scratch, we had repeat blocks.

1643
01:01:08,590 --> 01:01:12,640
So we wanted to repeat something,
let's say, seven times.

1644
01:01:12,640 --> 01:01:16,580
So we just said repeat seven, and
say I'm here to help you Snow White!

1645
01:01:16,580 --> 01:01:18,590

1646
01:01:18,590 --> 01:01:22,550
In C, we have for loops if we
want to go through something

1647
01:01:22,550 --> 01:01:23,970
a specific number of times.

1648
01:01:23,970 --> 01:01:29,700
Let's say if we initialize
the variable dwarves

1649
01:01:29,700 --> 01:01:35,410
and make sure-- so the first block
right there before the first semicolon,

1650
01:01:35,410 --> 01:01:39,260
we initialize our variable
to, and we set it to 0.

1651
01:01:39,260 --> 01:01:41,850
And our variable there
is an integer, int.

1652
01:01:41,850 --> 01:01:43,590

1653
01:01:43,590 --> 01:01:47,640
And the variable name is
dwarves, and we set dwarves to 0.

1654
01:01:47,640 --> 01:01:52,660
>> And the second part between the
two semicolons is our condition.

1655
01:01:52,660 --> 01:01:53,720

1656
01:01:53,720 --> 01:01:58,630
And so as long as dwarves
is less than seven,

1657
01:01:58,630 --> 01:02:01,730
we'll keep going through this for loop.

1658
01:02:01,730 --> 01:02:06,350
And then the last part is what do
we do at the end of this for loop?

1659
01:02:06,350 --> 01:02:12,480
dwarves ++, and that means we
increment dwarves by one every time.

1660
01:02:12,480 --> 01:02:13,900
>> So what's going to happen here?

1661
01:02:13,900 --> 01:02:15,860

1662
01:02:15,860 --> 01:02:17,620
So first we're going to go through.

1663
01:02:17,620 --> 01:02:19,690
We have dwarves as 0,
and then we're going

1664
01:02:19,690 --> 01:02:22,845
to print I'm here to
help you Snow White!

1665
01:02:22,845 --> 01:02:24,120

1666
01:02:24,120 --> 01:02:27,197
And then dwarves is going to
increase because we said dwarves ++.

1667
01:02:27,197 --> 01:02:28,409

1668
01:02:28,409 --> 01:02:29,450
Dwarves is going to be 1.

1669
01:02:29,450 --> 01:02:32,720
And then we compare-- dwarves is 1.

1670
01:02:32,720 --> 01:02:35,900
We compare it to is dwarves less than 7?

1671
01:02:35,900 --> 01:02:36,660
Yes.

1672
01:02:36,660 --> 01:02:38,320
I'm going to go through this again.

1673
01:02:38,320 --> 01:02:40,190
I'm here to help you Snow White!

1674
01:02:40,190 --> 01:02:44,490
And then dwarves becomes
2, and then we compare it.

1675
01:02:44,490 --> 01:02:46,621
Is 2 less that 7?

1676
01:02:46,621 --> 01:02:47,120
Yes.

1677
01:02:47,120 --> 01:02:48,740
We're going to keep going through.

1678
01:02:48,740 --> 01:02:51,395
And we're going to go
through this seven times.

1679
01:02:51,395 --> 01:02:52,980

1680
01:02:52,980 --> 01:02:59,290
>> So in the end, we're going to
have dwarves = 0 print out I'm

1681
01:02:59,290 --> 01:03:00,710
here to help you Snow White!

1682
01:03:00,710 --> 01:03:04,810
dwarves equals 1, 2, 3, 4, 5, and 6.

1683
01:03:04,810 --> 01:03:07,280
Remember we index at 0.

1684
01:03:07,280 --> 01:03:08,546
So we start with 0.

1685
01:03:08,546 --> 01:03:09,046
Yes?

1686
01:03:09,046 --> 01:03:11,630
>> STUDENT: So this is
different than the do

1687
01:03:11,630 --> 01:03:13,920
because this doesn't print
out initially at first.

1688
01:03:13,920 --> 01:03:15,880
So you could continue the same thing.

1689
01:03:15,880 --> 01:03:17,220

1690
01:03:17,220 --> 01:03:19,095
Could you do this also with the do loop?

1691
01:03:19,095 --> 01:03:20,450
Like the same process.

1692
01:03:20,450 --> 01:03:24,175
The condition is dwarves
less than 7 or whatever.

1693
01:03:24,175 --> 01:03:25,961
Response is less than 7.

1694
01:03:25,961 --> 01:03:27,335
SHARON: So you could technically.

1695
01:03:27,335 --> 01:03:30,360

1696
01:03:30,360 --> 01:03:34,210
So if we go back to-- your talking
about the while loop, right?

1697
01:03:34,210 --> 01:03:36,010
So the do while loop
is slightly different

1698
01:03:36,010 --> 01:03:39,966
because we guarantee at least
once that we'll go through it,

1699
01:03:39,966 --> 01:03:41,340
so that's the biggest difference.

1700
01:03:41,340 --> 01:03:50,330
But with the while loop we could
say while dwarves is less than 7,

1701
01:03:50,330 --> 01:03:53,310
do this, and then
increment dwarves by one.

1702
01:03:53,310 --> 01:03:58,660
And then we have to initialize
dwarves before this whole statement

1703
01:03:58,660 --> 01:04:00,628
that it equals 0.

1704
01:04:00,628 --> 01:04:02,128
So yeah, we could do that with that.

1705
01:04:02,128 --> 01:04:03,104
Mm-hm?

1706
01:04:03,104 --> 01:04:05,056
>> STUDENT: Can you go back to [INAUDIBLE]?

1707
01:04:05,056 --> 01:04:06,827

1708
01:04:06,827 --> 01:04:07,535
SHARON: For loop?

1709
01:04:07,535 --> 01:04:13,266
STUDENT: Yeah, so with the dwarves ++,
seems like that's what you do after

1710
01:04:13,266 --> 01:04:15,440
you've ran some other means.

1711
01:04:15,440 --> 01:04:16,106
SHARON: Correct.

1712
01:04:16,106 --> 01:04:18,380
STUDENT: Could you just
not have that and put it--

1713
01:04:18,380 --> 01:04:19,130
SHARON: You could.

1714
01:04:19,130 --> 01:04:23,770
STUDENT: So is [INAUDIBLE] right after
print out in the next line underneath.

1715
01:04:23,770 --> 01:04:25,430
SHARON: Yes, you could put it there.

1716
01:04:25,430 --> 01:04:27,952
But then you would
just leave that empty.

1717
01:04:27,952 --> 01:04:31,090
>> JASON HIRSCHHORN: You still
need the semi colon though.

1718
01:04:31,090 --> 01:04:34,194
>> SHARON: It looks a little awkward,
but you could technically do that.

1719
01:04:34,194 --> 01:04:35,118
Technically.

1720
01:04:35,118 --> 01:04:35,840
Please don't.

1721
01:04:35,840 --> 01:04:37,295

1722
01:04:37,295 --> 01:04:38,265
Yes?

1723
01:04:38,265 --> 01:04:40,687
>> STUDENT: Are there any
alternatives to ++?

1724
01:04:40,687 --> 01:04:42,145
Is there anything else [INAUDIBLE]?

1725
01:04:42,145 --> 01:04:52,990

1726
01:04:52,990 --> 01:04:54,825
>> SHARON: Technically it it's dwarves.

1727
01:04:54,825 --> 01:04:56,880

1728
01:04:56,880 --> 01:05:01,680
One equals sign we're going
to set it to dwarves plus 1.

1729
01:05:01,680 --> 01:05:03,670

1730
01:05:03,670 --> 01:05:06,762
So technically that's
what dwarves ++ means.

1731
01:05:06,762 --> 01:05:07,685
Does that make sense?

1732
01:05:07,685 --> 01:05:09,601
>> STUDENT: Yeah, but are
there any alternatives?

1733
01:05:09,601 --> 01:05:10,830
Like if you ever--

1734
01:05:10,830 --> 01:05:13,130
>> SHARON: Yeah, you could do dwarves - -.

1735
01:05:13,130 --> 01:05:14,280
>> STUDENT: [INAUDIBLE].

1736
01:05:14,280 --> 01:05:16,299
>> SHARON: Yeah, you could
do a host of things.

1737
01:05:16,299 --> 01:05:17,840
HANNAH: And you could increment by 2.

1738
01:05:17,840 --> 01:05:19,690
You could increment by 3.

1739
01:05:19,690 --> 01:05:23,120
Anything that's going to be changing,
it will eventually make the condition.

1740
01:05:23,120 --> 01:05:26,036
>> STUDENT: So if you wanted to increment
by 2, how would you write that?

1741
01:05:26,036 --> 01:05:27,060

1742
01:05:27,060 --> 01:05:31,400
>> HANNAH: You could either write dwarves--
you could write this whole thing out.

1743
01:05:31,400 --> 01:05:32,960
dwarves = dwarves + 2.

1744
01:05:32,960 --> 01:05:34,105
Or a slightly shorthand.

1745
01:05:34,105 --> 01:05:39,893
I'm just going to write + equals 2.

1746
01:05:39,893 --> 01:05:42,784
>> STUDENT: OK, and you'd write that
right where dwarves ++ is there.

1747
01:05:42,784 --> 01:05:43,450
HANNAH: Exactly.

1748
01:05:43,450 --> 01:05:44,116
SHARON: Correct.

1749
01:05:44,116 --> 01:05:45,297

1750
01:05:45,297 --> 01:05:46,421
There was another question?

1751
01:05:46,421 --> 01:05:47,383
Yeah?

1752
01:05:47,383 --> 01:05:49,788
>> STUDENT: [INAUDIBLE] dwarves ++?

1753
01:05:49,788 --> 01:05:52,484

1754
01:05:52,484 --> 01:05:53,400
SHARON: So you don't--

1755
01:05:53,400 --> 01:05:55,430
JASON HIRSCHHORN: Yeah, don't need
it there. [INAUDIBLE] very end.

1756
01:05:55,430 --> 01:05:57,250
So you do [INAUDIBLE]
ones because you're

1757
01:05:57,250 --> 01:06:01,810
kind of splitting up the initialization,
condition, and the change.

1758
01:06:01,810 --> 01:06:03,781
At the very end, you don't need it.

1759
01:06:03,781 --> 01:06:05,780
SHARON: Also notice you
don't need the semicolon

1760
01:06:05,780 --> 01:06:07,599
after the whole entire for loop.

1761
01:06:07,599 --> 01:06:09,531

1762
01:06:09,531 --> 01:06:14,361
>> STUDENT: How would you start with
an initial number of negative,

1763
01:06:14,361 --> 01:06:16,300
for example?

1764
01:06:16,300 --> 01:06:19,482
>> SHARON: You can initialize
dwarves equal to negative 2.

1765
01:06:19,482 --> 01:06:22,140
>> STUDENT: Do you just do dash 2?

1766
01:06:22,140 --> 01:06:24,270
>> SHARON: Yes, so the
negative sign, dash 2.

1767
01:06:24,270 --> 01:06:25,976

1768
01:06:25,976 --> 01:06:29,680
>> STUDENT: Is it [INAUDIBLE] to
initialize as dwarves [INAUDIBLE]?

1769
01:06:29,680 --> 01:06:30,340
>> SHARON: Yes.

1770
01:06:30,340 --> 01:06:35,630
So if we had just initialized dwarves
earlier, just do int dwarves semicolon,

1771
01:06:35,630 --> 01:06:39,300
and then there we can do
dwarves set that equal to 0.

1772
01:06:39,300 --> 01:06:43,184
>> STUDENT: Could we do it earlier in
the program saying int dwarves = 0,

1773
01:06:43,184 --> 01:06:44,590
and then just--

1774
01:06:44,590 --> 01:06:46,990
>> SHARON: Just not have-- so
there would be a space again,

1775
01:06:46,990 --> 01:06:48,531
but you would still need a semicolon.

1776
01:06:48,531 --> 01:06:49,500

1777
01:06:49,500 --> 01:06:50,890
Yeah.

1778
01:06:50,890 --> 01:06:51,494
Mm-hm?

1779
01:06:51,494 --> 01:06:54,285
STUDENT: Does this code say what
the value of dwarves is afterward.

1780
01:06:54,285 --> 01:06:58,030
If you ask it after all of this is
done to print the value of dwarves.

1781
01:06:58,030 --> 01:06:59,530
SHARON: You could ask it to do that.

1782
01:06:59,530 --> 01:07:00,191
STUDENT: OK.

1783
01:07:00,191 --> 01:07:02,190
SHARON: But you would
have to ask it to do that.

1784
01:07:02,190 --> 01:07:03,231
It doesn't do it for you.

1785
01:07:03,231 --> 01:07:04,730

1786
01:07:04,730 --> 01:07:06,875
I'm scared to put my earrings back in.

1787
01:07:06,875 --> 01:07:07,874

1788
01:07:07,874 --> 01:07:09,290
Do it at the end for the applause.

1789
01:07:09,290 --> 01:07:10,090
Just kidding.

1790
01:07:10,090 --> 01:07:11,755
>> JASON HIRSCHHORN: So that's the same.

1791
01:07:11,755 --> 01:07:13,460
So initialize at the top.

1792
01:07:13,460 --> 01:07:15,360
Condition, print, change.

1793
01:07:15,360 --> 01:07:22,482
So this is exactly the same as
that if anybody can see that.

1794
01:07:22,482 --> 01:07:23,871

1795
01:07:23,871 --> 01:07:26,370
STUDENT: Why don't you have the
semicolon on the first line?

1796
01:07:26,370 --> 01:07:27,657

1797
01:07:27,657 --> 01:07:28,240
SHARON: Where?

1798
01:07:28,240 --> 01:07:29,490
STUDENT: After the first line.

1799
01:07:29,490 --> 01:07:31,976
SHARON: After the 4 in the parentheses?

1800
01:07:31,976 --> 01:07:33,850
Because we want to go
through into this loop.

1801
01:07:33,850 --> 01:07:39,309
And if you take a look at loops in
general, they don't have semicolons.

1802
01:07:39,309 --> 01:07:40,100
It's not practical.

1803
01:07:40,100 --> 01:07:45,160

1804
01:07:45,160 --> 01:07:46,240
Are we good?

1805
01:07:46,240 --> 01:07:47,470
One more question, two more.

1806
01:07:47,470 --> 01:07:48,056
Yeah?

1807
01:07:48,056 --> 01:07:49,930
STUDENT: This might be
a little bit advanced,

1808
01:07:49,930 --> 01:07:52,840
but do dwarves have a
different [INAUDIBLE]

1809
01:07:52,840 --> 01:07:54,780
from a variable [INAUDIBLE].

1810
01:07:54,780 --> 01:07:57,421

1811
01:07:57,421 --> 01:07:58,170
SHARON: Very good.

1812
01:07:58,170 --> 01:07:59,045
STUDENT: [INAUDIBLE].

1813
01:07:59,045 --> 01:08:00,480

1814
01:08:00,480 --> 01:08:02,456
>> SHARON: Yes, it is.

1815
01:08:02,456 --> 01:08:03,794

1816
01:08:03,794 --> 01:08:04,422
What?

1817
01:08:04,422 --> 01:08:05,880
JASON HIRSCHHORN: Yeah, so it does.

1818
01:08:05,880 --> 01:08:08,965
So normally the scope of
something is in the curly braces.

1819
01:08:08,965 --> 01:08:10,216

1820
01:08:10,216 --> 01:08:12,340
So scope is always going
to be in the curly braces,

1821
01:08:12,340 --> 01:08:14,850
but that wouldn't make
much sense for the for loop

1822
01:08:14,850 --> 01:08:17,550
because we initialized
dwarves in that curly brace.

1823
01:08:17,550 --> 01:08:23,310
So normally the scope of dwarves, that
variable wouldn't extend past that.

1824
01:08:23,310 --> 01:08:25,000
This is a special case though.

1825
01:08:25,000 --> 01:08:28,080
So you initialize it
within those parentheses,

1826
01:08:28,080 --> 01:08:30,600
and then you have the scope later on.

1827
01:08:30,600 --> 01:08:32,720
So special case.

1828
01:08:32,720 --> 01:08:39,059
They should not have that, and
that was-- That make sense?

1829
01:08:39,059 --> 01:08:40,037
>> STUDENT: No.

1830
01:08:40,037 --> 01:08:41,629
>> JASON HIRSCHHORN: I can go over it.

1831
01:08:41,629 --> 01:08:43,170
So what are you still confused about?

1832
01:08:43,170 --> 01:08:47,200
>> STUDENT: As in can you use dwarves-- you
can obviously use dwarves [INAUDIBLE]

1833
01:08:47,200 --> 01:08:48,439
outside the formula too?

1834
01:08:48,439 --> 01:08:49,480
>> JASON HIRSCHHORN: No, no.

1835
01:08:49,480 --> 01:08:53,385
So the scope of it is only inside the
curly braces for the for loop, yeah.

1836
01:08:53,385 --> 01:08:56,509

1837
01:08:56,509 --> 01:08:59,300
SHARON: But if you initialize
dwarves outside of the for loop, then

1838
01:08:59,300 --> 01:09:05,021
you can use it elsewhere
There's one more question?

1839
01:09:05,021 --> 01:09:05,520
No?

1840
01:09:05,520 --> 01:09:09,529

1841
01:09:09,529 --> 01:09:10,130
OK.

1842
01:09:10,130 --> 01:09:15,807
>> So we talked a little bit about nesting
for loops or nesting conditionals,

1843
01:09:15,807 --> 01:09:16,390
if statements.

1844
01:09:16,390 --> 01:09:17,660

1845
01:09:17,660 --> 01:09:21,310
So here's an example of where
we could nest a for loop.

1846
01:09:21,310 --> 01:09:26,500
Let's say we were printing
this table of x's right here.

1847
01:09:26,500 --> 01:09:31,430
We might want to-- first if
we just don't look at the code

1848
01:09:31,430 --> 01:09:34,329
and we just think about it, we
want to go through every row

1849
01:09:34,329 --> 01:09:36,550
and print each column, right?

1850
01:09:36,550 --> 01:09:37,854

1851
01:09:37,854 --> 01:09:38,729
Does that make sense?

1852
01:09:38,729 --> 01:09:39,787

1853
01:09:39,787 --> 01:09:40,286
OK.

1854
01:09:40,286 --> 01:09:41,439

1855
01:09:41,439 --> 01:09:44,809
>> So here we're going through
every row for basically each row,

1856
01:09:44,809 --> 01:09:45,850
and there are three rows.

1857
01:09:45,850 --> 01:09:47,149

1858
01:09:47,149 --> 01:09:50,806
And then within each row
for each column, and there

1859
01:09:50,806 --> 01:09:53,149
are four columns, print an x.

1860
01:09:53,149 --> 01:09:55,920

1861
01:09:55,920 --> 01:09:56,420
so.

1862
01:09:56,420 --> 01:10:02,400
When row is 0 and column
is 0, we print this x.

1863
01:10:02,400 --> 01:10:06,920
And then we keep going
through the column loop.

1864
01:10:06,920 --> 01:10:08,300

1865
01:10:08,300 --> 01:10:11,280
Row is still 0, but column is one.

1866
01:10:11,280 --> 01:10:13,760
And then column is 2,
and then column is 3.

1867
01:10:13,760 --> 01:10:14,770

1868
01:10:14,770 --> 01:10:19,270
And then we exit out of that
loop because then column

1869
01:10:19,270 --> 01:10:20,605
is no longer less than 4.

1870
01:10:20,605 --> 01:10:21,970

1871
01:10:21,970 --> 01:10:25,330
And then we print a new line,
and we go to the new line.

1872
01:10:25,330 --> 01:10:30,160
And then we go through the next
row, and row gets incremented,

1873
01:10:30,160 --> 01:10:31,885
and we go through that again.

1874
01:10:31,885 --> 01:10:32,760
Does that make sense?

1875
01:10:32,760 --> 01:10:34,120

1876
01:10:34,120 --> 01:10:34,778
Yes?

1877
01:10:34,778 --> 01:10:40,150
>> STUDENT: So to nest [INAUDIBLE] is
just putting it inside of the for loop?

1878
01:10:40,150 --> 01:10:44,290
>> SHARON: So nesting means that we
have a for loop within a for loop,

1879
01:10:44,290 --> 01:10:45,382
like Inception.

1880
01:10:45,382 --> 01:10:47,798
>> STUDENT: You don't need a
special rotation or anything?

1881
01:10:47,798 --> 01:10:49,567
You just stick it right inside of it?

1882
01:10:49,567 --> 01:10:50,233
SHARON: Correct.

1883
01:10:50,233 --> 01:10:52,060

1884
01:10:52,060 --> 01:10:52,560
Yes?

1885
01:10:52,560 --> 01:10:56,050
>> STUDENT: Might be [INAUDIBLE], but
it looks like there's an extra space

1886
01:10:56,050 --> 01:10:57,730
between all the x's.

1887
01:10:57,730 --> 01:11:01,197
I don't know if that's-- If that
were to actually do the program,

1888
01:11:01,197 --> 01:11:02,530
would it do something like that?

1889
01:11:02,530 --> 01:11:03,320
>> SHARON: So no.

1890
01:11:03,320 --> 01:11:04,970
That was pressing Enter.

1891
01:11:04,970 --> 01:11:06,360

1892
01:11:06,360 --> 01:11:08,342
That was bad on our part.

1893
01:11:08,342 --> 01:11:08,842
Apologize.

1894
01:11:08,842 --> 01:11:11,576
>> HANNAH: How would you change this
program if you did one extra line?

1895
01:11:11,576 --> 01:11:12,451
>> STUDENT: [INAUDIBLE].

1896
01:11:12,451 --> 01:11:13,932

1897
01:11:13,932 --> 01:11:14,640
SHARON: Good job.

1898
01:11:14,640 --> 01:11:16,067

1899
01:11:16,067 --> 01:11:19,150
STUDENT: You can also print the same
thing by switching around the column,

1900
01:11:19,150 --> 01:11:20,632
right?

1901
01:11:20,632 --> 01:11:21,620
>> SHARON: Hm?

1902
01:11:21,620 --> 01:11:27,054
>> STUDENT: So to print your little
xxx, the first line can say print,

1903
01:11:27,054 --> 01:11:30,020
and instead of saying
row, it says column.

1904
01:11:30,020 --> 01:11:32,710
>> SHARON: So you could change
the variable names to do that.

1905
01:11:32,710 --> 01:11:33,836
Is that what you're saying?

1906
01:11:33,836 --> 01:11:36,175
>> STUDENT: No, I'm just
saying that-- so you're

1907
01:11:36,175 --> 01:11:38,354
printing rows first and
then printing columns.

1908
01:11:38,354 --> 01:11:43,010
Can you also print columns first and
then rows to get the same diagram?

1909
01:11:43,010 --> 01:11:44,760
SHARON: You could, but
then you would have

1910
01:11:44,760 --> 01:11:47,370
to be careful of where
you put the new line.

1911
01:11:47,370 --> 01:11:48,876
And how would you jump back?

1912
01:11:48,876 --> 01:11:55,082

1913
01:11:55,082 --> 01:11:56,790
JASON HIRSCHHORN: If
you just switched it

1914
01:11:56,790 --> 01:12:01,190
and the values were different,
instead of having four-- what is it?

1915
01:12:01,190 --> 01:12:02,530
Three by four.

1916
01:12:02,530 --> 01:12:08,955
I You would have four
rows and three columns.

1917
01:12:08,955 --> 01:12:09,830
Does that make sense?

1918
01:12:09,830 --> 01:12:10,270
>> STUDENT: Yeah.

1919
01:12:10,270 --> 01:12:11,610
>> JASON HIRSCHHORN: So
yeah, you could do that.

1920
01:12:11,610 --> 01:12:12,318
Yeah, definitely.

1921
01:12:12,318 --> 01:12:12,461

1922
01:12:12,461 --> 01:12:15,710
SHARON: But that would be literally just
switching the names of the variables.

1923
01:12:15,710 --> 01:12:19,930

1924
01:12:19,930 --> 01:12:20,430
Good?

1925
01:12:20,430 --> 01:12:21,461

1926
01:12:21,461 --> 01:12:21,960
OK.

1927
01:12:21,960 --> 01:12:23,970

1928
01:12:23,970 --> 01:12:26,120
All right, P set one.

1929
01:12:26,120 --> 01:12:32,399
OK, so the first part of it
you will be doing this, Mario.

1930
01:12:32,399 --> 01:12:32,940
Just kidding.

1931
01:12:32,940 --> 01:12:34,210
It's more like this.

1932
01:12:34,210 --> 01:12:39,350
And so when we just looked at the
nested for loops, making that table,

1933
01:12:39,350 --> 01:12:45,960
think about how you might be able to
print out these hashtags in this way.

1934
01:12:45,960 --> 01:12:50,090
And then right here how would you
print this right here, this open space.

1935
01:12:50,090 --> 01:12:51,429
>> STUDENT: [INAUDIBLE].

1936
01:12:51,429 --> 01:12:52,970
SHARON: Yeah, you just print a space.

1937
01:12:52,970 --> 01:12:54,720
OK, so just think about that.

1938
01:12:54,720 --> 01:12:56,699

1939
01:12:56,699 --> 01:12:58,740
HANNAH: And then the same
part of the problem set

1940
01:12:58,740 --> 01:13:01,630
is a program called
greedy.c, so that you're

1941
01:13:01,630 --> 01:13:03,810
going to want to think
about conditionals

1942
01:13:03,810 --> 01:13:06,960
and making sure that you
can make proper change.

1943
01:13:06,960 --> 01:13:10,780
And one little warning we have for you
is be careful of floating point values.

1944
01:13:10,780 --> 01:13:14,530
If that means absolutely nothing to you,
it'll be covered in lecture this week

1945
01:13:14,530 --> 01:13:16,410
and also in [INAUDIBLE]
walk through, which

1946
01:13:16,410 --> 01:13:20,420
you guys will learn to
love on the problem sets.

1947
01:13:20,420 --> 01:13:23,470
>> One thing that I really suggest,
especially with Mario.c,

1948
01:13:23,470 --> 01:13:26,110
when you're doing the problem
set, if you get stuck,

1949
01:13:26,110 --> 01:13:28,460
start by doing it on paper.

1950
01:13:28,460 --> 01:13:31,960
Write it out and actually sit there
and pretend to be the computer,

1951
01:13:31,960 --> 01:13:36,530
and go through-- say
I were the computer,

1952
01:13:36,530 --> 01:13:38,380
how would I follow
this for loop through?

1953
01:13:38,380 --> 01:13:41,260
How would my variables
in the for loop change?

1954
01:13:41,260 --> 01:13:43,640
So doing it on paper
makes it 10 times easier

1955
01:13:43,640 --> 01:13:45,710
when you go to sit down at the computer.

1956
01:13:45,710 --> 01:13:46,840
So just my little plug.

1957
01:13:46,840 --> 01:13:50,060
>> SHARON: And also don't think that you
have to code everything all at once.

1958
01:13:50,060 --> 01:13:53,060
Make sure you take an iterative process.

1959
01:13:53,060 --> 01:13:55,430
Do a little bit, print
it out, see what happens.

1960
01:13:55,430 --> 01:13:57,044

1961
01:13:57,044 --> 01:13:58,710
Sometimes it's a little trial and error.

1962
01:13:58,710 --> 01:14:00,220

1963
01:14:00,220 --> 01:14:01,375
And come to office hours.

1964
01:14:01,375 --> 01:14:01,875
Super fun.

1965
01:14:01,875 --> 01:14:02,472

1966
01:14:02,472 --> 01:14:03,930
JASON HIRSCHHORN: So any questions?

1967
01:14:03,930 --> 01:14:05,186

1968
01:14:05,186 --> 01:14:07,317
All right guys, that
was your first section.

1969
01:14:07,317 --> 01:14:08,400
HANNAH: Thanks for coming.

1970
01:14:08,400 --> 01:14:09,106
JASON HIRSCHHORN: Thanks for come.

1971
01:14:09,106 --> 01:14:09,890
SHARON: Thank you.

1972
01:14:09,890 --> 01:14:11,440
[APPLAUSE]

1973
01:14:11,440 --> 01:14:15,915