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DAVID MALAN: All right.

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Looks like we have just
about everyone back.

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Well, if you just joined, welcome
to the CS50 Educator Workshop.

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My name is David Malan, and I teach this
course here at Harvard in Cambridge,

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Massachusetts called CS50.

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We started these workshops
over five years ago

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now, toward an end of just making
it easier for teachers like us,

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like you, to adopt or adapt
introductory materials like CS50 Zone.

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The course has since evolved
into multiple different flavors,

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as you may know.

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Not only the version that we
offer here, traditionally,

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on campus, but also online through
Harvard's Extension School for adults.

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And others as a massive open
online course through edX,

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as well as now some Follow On
and some precursor courses.

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Some of which you might be familiar
with, like CS50's Introduction

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to Technology, Computer Science
for Business Professionals;

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Follow On courses on game
development, web development,

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artificial intelligence, and more.

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So indeed, particularly at the
k-12 level, or maybe 7 to 12 level,

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have we really been
focusing in recent years,

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on making sure teachers
have more runway.

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So that they can actually put together
using some of their own materials

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and perhaps some of ours, a
full three or four year program.

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Particularly for younger students,
and now older students as well.

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So this workshop, being
online, just like last summer.

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We're taking for granted that
folks are familiar with the course

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in various aspects per Carter's
emails over the past couple of weeks.

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There were materials from
last summer, that we again

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made available this summer, just to help
on-board folks do some of the basics.

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So today and tomorrow,
we'll generally assume

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that folks are already familiar
with CS50 in all of its forms

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to some extent.

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And indeed, this weekend will be as
hands on and as discussion oriented

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as we can make it.

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So that you feel like, Zoom
wise, it's as high value

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as we can do things online these days.

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Before we dive into this
morning's first session,

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wanted to make a few introductions.

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I'm joined here ultimately
by CS50's own Brian

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Yu, who you might know from the web
class, the AI class, and CS50 itself.

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But let me first introduce you to
two of our newest team members,

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one of whom you've heard
from email already.

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Carter Zenke and Bernie
Longboy, who have

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joined us now on the
team here in Cambridge

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to focus particularly on
a lot of these outreach

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and AP high school and older efforts.

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Carter, over to you.

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CARTER ZENKE: Hello, everyone.

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It's so wonderful to see
you all in one place.

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I'm really excited for this
workshop we have together.

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As David has said, and I've been
saying over our emails together,

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this is intended to be
a celebration of all

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of our work as educators and
as teachers involved with CS50.

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To that end, today we
have several presentations

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from educators who have
deeply thought about how

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to make their CS50
classrooms as engaging

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and transformative as possible.

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And we'll also have some dedicated
sessions for you to meet each other,

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and talk about your own
experiences teaching CS50,

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and how you can further
improve your practice.

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I'm really excited to see what we'll
all talk about during our workshop

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together.

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Thank you all for being here.

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Excited to do it.

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BERNIE LONGBOY: Good morning, everyone.

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I just want to welcome everyone as well.

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And look forward to this weekend.

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I'm very excited with you
all to learn so much too.

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So have a great, great
morning this morning.

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DAVID MALAN: And for those
who might not know him--

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Brian, do you want to say
a formal hello as well?

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BRIAN YU: Sure.

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Hi, everyone.

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It's so good to be here at
another CS50 Educator workshop.

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I first attended my first
Educator workshop back in 2016.

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And every year I've been to one,
it's been amazing to see the ideas

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that educators have
been able to bring up,

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and thinking about how
best to support students

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as they learn computer science.

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So, it's so good to see
everyone here this weekend.

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DAVID MALAN: Indeed, welcome.

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So within the breakout
groups and smaller sessions,

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you'll definitely have an
opportunity to meet others.

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Feel free to use the chat window
though throughout today and tomorrow

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to just say hello.

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In fact, if you'd like to
say right now, as some of you

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already have, "Hello", from
wherever in the world you are.

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It's always quite fun to see just
what's breadth of teachers are able now,

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especially that things are
online, to attend with us.

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For this first morning
session here in Cambridge,

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we thought we would offer
something called "CS50 Explained,

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Behind the Pedagogy".

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In part, the goal here is to answer in
one fell swoop as many frequently asked

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questions as we can.

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Particularly some that we've
seen in workshops past.

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And also to resurrect
something, or evoke really,

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something that we started
doing a few years ago.

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Where a colleague and I
would actually rewatch

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CA50 Zone lectures, and
talk about the "Why".

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Students typically are more
interested, daresay, in the "What",

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and just making sure that they're
comprehending what it is we or you

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might be presenting in the classroom.

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But for teachers sake,
we thought we would

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try to peel back the curtain a bit.

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And give you a look at, or some
justification for, "why" we in CS50

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do some of the things the way we do.

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We don't claim that these are
necessarily the right ways,

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we can only argue that this is
the reason we do things and why.

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But by all means, feel free to interject
throughout this morning session

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with any questions in the chat,
any virtual hands in Zoom,

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and certainly feel free to raise some
of these same questions in later today's

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sessions as well.

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Brian, shall I turn
the floor over to you?

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And Brian and I will have
a conversation of sorts,

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even though both he and I
rather know where this is going.

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But again, please do
interject at any point.

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Brian?

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BRIAN YU: So I thought we would
start with one of the topics

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that I think a lot of people ask
about when they first hear about CS50

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and CS50's curriculum.

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And that is the programming
languages that CS50 ends up using.

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So I see on your slide that CS50
covers a lot of different languages--

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Scratch, and C, and Python;
SQL, HTML, CSS, and JavaScript.

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So that's a lot of different languages.

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Well, another reasonable
approach might be

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for spending an entire
course diving deeply

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into one language like
just C or just Python.

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So I was hoping you could
maybe tell us a little bit

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about your thinking behind
choosing these languages,

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and multiple different
languages for the class.

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DAVID MALAN: So, it's a
really good question, Brian.

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I'm glad you brought this on up.

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So, I think CS50 here at Harvard
has been around for some 30 years.

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And back when I took it
myself, some 20+ years ago,

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I feel like I and a lot of students
emerged from the class in an earlier

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form of it, thinking of
the class as a course in C.

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And indeed, at the time, it
pretty much only focused on C

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throughout the entire semester.

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And so, as a result, I and I
think some of my classmates

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emerged, ultimately, with a mental
model of "I know how to program in C"

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or "I took a C class".

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And the downside of this is, that
certainly with a language like C,

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it's not one that you would
typically reach for off-the-shelf

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to solve problems.

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Generally, after taking a course in
it, unless you're a lower level systems

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type programmer-- and we, in
retrospect, I wish I had been,

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I had appreciated as a student
that what I really did learn

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was not just how to program in C,
but to how to program more generally.

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But what I didn't have at
the time was an opportunity

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to try to apply some of the
lessons in that original course

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to just other domains.

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And pick up languages with the
support structure of a professor

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and a whole teaching
staff, teaching assistants,

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some of my undergraduate classmates.

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And so, when I took over
the course some years later,

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and this is now 16 years ago, I
had just exited graduate school.

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Where I had the opportunity
to take a class at MIT's

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Media Lab, where they
had literally just been

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beta testing Scratch, this graphical
language, for the very first time.

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And we were using it in the
graduate course I was taking.

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And so, when I finished grad school
and then started teaching CS50 a year

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or two later, we added Scratch to
the very beginning of the course.

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And the goal was, to send a message
very early on that, one, programming

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doesn't need to seem or be daunting.

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It doesn't need to look scary textually
with parentheses, and semicolons,

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and the like.

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Scratch, from day one,
allowed us to start

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focusing on concepts-- on functions,
variables, conditions, loops

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and the like without the
distraction of any more

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textual based languages distractions.

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Thereafter, I have always felt that
C provides a very solid foundation

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from the ground up.

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It's not without its
downsides, of course,

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in that memory management
pointers and the like

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tend to get very sophisticated.

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But insofar as CS50, both
for us here on campus

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and for a lot of people online
who've been taking it for some years,

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is a terminal class.

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It's the one class that
they take, from which

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they want to get some practical skills.

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They want to have an
ability to program, but they

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don't want to become computer
scientists themselves.

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So they might not necessarily go down
the rabbit hole of other courses.

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We wanted to introduce students
to another procedural language

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or language that has procedural
aspects, namely Python.

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Years ago, it was PHP.

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Now, it's Python.

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And Python is just
wonderfully multipurpose.

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You can use it for command line
applications, web applications, data

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science applications nowadays.

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And so it's just a nice fit for
the message that we want to send.

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And then at the tail end
of the class, we also

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want students to understand the
applicability of computer science.

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And to programming, to just
something they see and use every day

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in web programming.

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Just really does resonate,
certainly with our population here,

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and it seems, at large.

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Unfortunately, to
introduce web programming,

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you need this additional
fire hose of content.

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Not just HTML and CSS
to do static stuff,

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but you ideally want to
add in a little JavaScript

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these days, so that you can do some
things interactively in the GUI.

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And honestly, you ideally
want some place to put data,

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so that you can actually
build proper applications

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that live on beyond the course,
and for that we need SQL.

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So we can see, it is a lot.

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And students don't become an
expert in any one of these.

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But nowadays, I do
dare say that students

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exit the class with a mental model
of having learned how to program.

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Not program in all
paradigms, we don't really

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touch much OO or functional programming,
if you're familiar with those.

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But they absolutely
learn, pretty rigorously,

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how to program
procedurally, so to speak.

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Brian?

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BRIAN YU: And looking at that
list, it seems like the--

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maybe one that you might least expect
to see on a typical introductory course

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is the one on C. Like you mentioned,
that C's been around in CS50

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since CS50 was first
introduced at Harvard.

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And I was wondering if you could
talk about why it stayed there.

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C is definitely, maybe, less
popular now than it was before.

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And can you talk a little
bit about the rationale

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behind what role C serves inside of
this computer science curriculum?

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DAVID MALAN: So I do think that C
is about as close to the hardware,

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so to speak, as you can
get before things really

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get scary with something called Assembly
language and the lower level machine

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instructions that are ultimately
getting executed by the computer's CPU.

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C doesn't really have much in the way
of libraries right out of the box,

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like a Python, like
Java, even like C+ has.

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And so, if you want
something to exist in C,

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you pretty much need to
implement it yourself.

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Or at least there isn't a
standard library in the same way

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as there is with other languages.

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That if you want a linked list, you grab
it over here, if you want a hash table,

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you grab it over here.

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And so, it's a nice language in
that syntactically or grammatically,

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it's relatively small.

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And with the couple of exceptions,
students pretty much in CS50

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see all syntactic
features of the language,

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minus things like unions
and function pointers.

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But for the most part, students
then use this language,

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and ultimately have an
understanding of what's really going

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on underneath the hood of the computer.

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The memory management stuff can get
into the weeds for many students,

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but at the end of the day,
you realize that all you

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have is this canvas of bytes.

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Zeros and ones, or decimal digits,
however you want to think about it.

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And you can use those
however you see fit.

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So as complicated as all of
today's software is that we write

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or that we might use on
our computers, it all

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reduces to that very simple canvas.

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And I think as a result, students exit
CS50 not just thinking, hopefully,

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that they are budding
software developers.

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But that they're budding engineers, and
they're budding computer scientists,

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because they really have
this bottom up understanding.

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And my favorite moment still,
both in PHP and now Python,

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is when we go in one week having
students implement with the Speller

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problem set, if you're familiar, their
very own hash table storing words

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from a big dictionary.

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And then the next week, do
we distill that same program

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into eight lines of Python code.

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One line is what gives us the
hash table or the dictionary.

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And I think, what an amazing way to
emphasize the notion of abstraction

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than to show students that we can
take those previous several weeks

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and now condense them
into a language feature.

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BRIAN YU: A few people in chat
are mentioning that figuring out

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hash tables was really confusing.

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Yeah, I remember
struggling a lot when I was

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first trying to implement my
own hash table from scratch,

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working on this very assignment.

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But then, I also
remember seeing in Python

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the first time, how you can do all of
that in just a couple of lines of code.

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And really appreciating what it is that
these higher level languages are also

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able to offer.

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And definitely at any point,
I'm asking David questions.

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But if you have questions for
me or David as well, definitely

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feel free to raise your virtual hand in
Zoom, or type the question in the chat

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that I can relay to David as well.

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So if you have questions about CS50
and why the course does things the way

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that the course does things,
happy to talk about those too.

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AHMAD ESSAYED: Hi, David.

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Hi, Brian.

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Hi, everyone.

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My question is about the shorts.

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Sometimes the shorts, I feel they--

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sometimes they're helpful, but sometimes
they are adding more confusion.

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So, sometimes David
is covering one topic,

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but this topic needs more information.

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00:13:20,950 --> 00:13:25,120
And David is leaving that
to the shorts to cover.

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But I have the feeling
that students sometimes

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need this to be covered in
the lecture itself by David.

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So what's the rationale behind shorts,
why not do it all in the lecture?

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And some of the shorts,
they actually need

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00:13:43,270 --> 00:13:46,348
to be discussed before the lectures.

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Before the lecture.

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00:13:47,140 --> 00:13:49,557
Some of them, they need to be
discussed after the lecture.

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And there is no roadmap for students.

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So they assume that they watch
the lecture, then the shorts.

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But some of the topics in the shorts--

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I feel that they should have been
covered before the lecture itself.

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00:14:03,420 --> 00:14:04,078
So--

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00:14:04,078 --> 00:14:05,120
DAVID MALAN: Interesting.

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In the chat, Ahmad, do you
mind proposing a few examples?

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00:14:07,650 --> 00:14:10,010
But in the meantime, I
can respond in general.

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00:14:10,010 --> 00:14:13,850
So, at least the way the traditional
class here is structured on campus,

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00:14:13,850 --> 00:14:16,010
we have certain constraints like time.

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Like the duration that a lecture can be.

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And the function of lectures,
generally in our view,

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is to create this
narrative for the week.

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To introduce students to a range of
concepts that will then be explored

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00:14:26,990 --> 00:14:28,730
in some form on the problem set.

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00:14:28,730 --> 00:14:31,040
But we don't have the
luxury, just practically

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00:14:31,040 --> 00:14:32,900
speaking, to go down every rabbit hole.

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00:14:32,900 --> 00:14:36,530
Or to focus as much as we might
like in an ideal world on each

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00:14:36,530 --> 00:14:39,140
of those topics in depth
during that one seeding.

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00:14:39,140 --> 00:14:42,410
So the approach we've taken over
time, is to then define these shorts.

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Which, if unfamiliar, are
indeed these shorter videos

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00:14:44,660 --> 00:14:46,827
generally taught by a
colleague of ours, Doug Lloyd,

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00:14:46,827 --> 00:14:48,290
against a nice white backdrop.

321
00:14:48,290 --> 00:14:51,140
Wherein he focuses
entirely on one topic--

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00:14:51,140 --> 00:14:54,980
so this is a topic on linked
list, this is a short on arrays,

323
00:14:54,980 --> 00:14:56,990
this is a short on some other topic.

324
00:14:56,990 --> 00:15:00,860
And the goal there is to, one,
indeed go down the rabbit hole

325
00:15:00,860 --> 00:15:02,390
of those individual topics.

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And also, frankly, pedagogically,
to give students another person's

327
00:15:05,630 --> 00:15:07,710
perspective on the same topic.

328
00:15:07,710 --> 00:15:11,270
It's not just a rehash of the exact
same examples, the exact same style.

329
00:15:11,270 --> 00:15:13,910
It's Doug's own take
on that same material.

330
00:15:13,910 --> 00:15:17,270
Much like a student in our
on-campus sections, or recitations,

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00:15:17,270 --> 00:15:18,770
would see different exposure.

332
00:15:18,770 --> 00:15:20,870
I think, pragmatically
speaking, if you're

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00:15:20,870 --> 00:15:24,410
finding that certain shorts
should come before a lecture,

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00:15:24,410 --> 00:15:27,410
please do mention as much in the
chat, or email me and Brian afterward.

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00:15:27,410 --> 00:15:28,770
Because that's an easy fix.

336
00:15:28,770 --> 00:15:31,817
We can certainly guide students
toward that more correctly.

337
00:15:31,817 --> 00:15:32,900
But that's not the intent.

338
00:15:32,900 --> 00:15:35,870
Generally, they're meant to be
supplementary, optional resources

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00:15:35,870 --> 00:15:38,120
for students if they
want to dive in deeper

340
00:15:38,120 --> 00:15:42,120
to topics we looked at that week.

341
00:15:42,120 --> 00:15:44,310
Brian, if you don't mind
my turning the tables here,

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00:15:44,310 --> 00:15:47,417
because you've given quite a bit
of thought to how we grade in CS50.

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And we grade in different ways based
on the demographic of students,

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whether they're the
traditional on-campus

345
00:15:51,810 --> 00:15:53,727
students, or the online
students, or certainly

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via the massive open online course.

347
00:15:55,820 --> 00:15:58,320
It's a different experience to
some extent for the students,

348
00:15:58,320 --> 00:16:02,190
as to just how much feedback we can
viably provide tens of thousands

349
00:16:02,190 --> 00:16:03,330
of students online.

350
00:16:03,330 --> 00:16:06,750
So, Brian, we've generally
presented to teachers in the past,

351
00:16:06,750 --> 00:16:08,490
that we take this
three pronged approach.

352
00:16:08,490 --> 00:16:11,400
Three axis of correctness,
design, and style.

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00:16:11,400 --> 00:16:14,130
Do you want to speak to exactly
what we mean by those three,

354
00:16:14,130 --> 00:16:17,065
and why we use those three?

355
00:16:17,065 --> 00:16:19,440
BRIAN YU: So these are the
three things that we generally

356
00:16:19,440 --> 00:16:22,357
ask students to think about when
they're working on their assignments.

357
00:16:22,357 --> 00:16:26,340
And the first one, and arguably the
most important one, is just correctness.

358
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Which in our mind of
answering the question--

359
00:16:28,440 --> 00:16:32,400
does the student's code do,
what our problem specification

360
00:16:32,400 --> 00:16:34,170
asked for the student's program to do?

361
00:16:34,170 --> 00:16:38,670
If we're asking them to build a pyramid
made out of hash marks and spaces,

362
00:16:38,670 --> 00:16:41,280
are they using the right arrangement
of hash marks and spaces?

363
00:16:41,280 --> 00:16:43,740
If they're building a spell
checker, does it correctly

364
00:16:43,740 --> 00:16:45,720
identify the words that are misspelled?

365
00:16:45,720 --> 00:16:50,190
And it used to be the case that
for correctness, I would manually

366
00:16:50,190 --> 00:16:52,320
test and run each of
my students' programs,

367
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and test it on various different inputs.

368
00:16:54,850 --> 00:16:57,930
But now, we've built
this tool called check50,

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00:16:57,930 --> 00:16:59,940
which can be used by
students and educators

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00:16:59,940 --> 00:17:02,610
alike to do some automated
assessment of correctness.

371
00:17:02,610 --> 00:17:05,579
And that's really helped to
improve the speed at which we

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00:17:05,579 --> 00:17:07,480
can get some feedback back to students.

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00:17:07,480 --> 00:17:10,740
So students can be working on their
own time, working on a problem,

374
00:17:10,740 --> 00:17:13,200
and run this tool, check50, to see--

375
00:17:13,200 --> 00:17:15,359
have I really managed
to solve this problem?

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00:17:15,359 --> 00:17:18,630
Or are there maybe some edge
cases that I haven't considered,

377
00:17:18,630 --> 00:17:21,480
or some bug in the program
that I haven't quite noticed.

378
00:17:21,480 --> 00:17:25,050
And check50 can help students to think
about the correctness of their program

379
00:17:25,050 --> 00:17:26,770
there as well.

380
00:17:26,770 --> 00:17:29,790
But we don't really want
students to just stop there.

381
00:17:29,790 --> 00:17:33,180
That there are many ways to
write a correct program that

382
00:17:33,180 --> 00:17:34,720
solves the problem.

383
00:17:34,720 --> 00:17:37,080
But some ways are going to
be better than other ways.

384
00:17:37,080 --> 00:17:40,950
Better in terms of the efficiency and
how long the program takes to run.

385
00:17:40,950 --> 00:17:44,310
Better in terms of the overall
organization of the code

386
00:17:44,310 --> 00:17:48,510
and whether it's logical and makes
sense, and other considerations

387
00:17:48,510 --> 00:17:52,170
that we generally categorize under
the second heading of design.

388
00:17:52,170 --> 00:17:56,340
And design, then, is all about
how well written is the code.

389
00:17:56,340 --> 00:17:59,260
Even if regardless of
whether it's correct or not.

390
00:17:59,260 --> 00:18:03,240
Are they making good use of programming
constructs like loops and conditions

391
00:18:03,240 --> 00:18:04,950
where it's appropriate to do so.

392
00:18:04,950 --> 00:18:07,380
Are they repeating
themselves a lot when it

393
00:18:07,380 --> 00:18:09,300
might be better to create
a different function

394
00:18:09,300 --> 00:18:11,217
to do some of that same behavior.

395
00:18:11,217 --> 00:18:13,050
And so, here is where
really the opportunity

396
00:18:13,050 --> 00:18:15,180
is to teach good design practices.

397
00:18:15,180 --> 00:18:18,580
Teaching not only how to write
code, but how to write code well.

398
00:18:18,580 --> 00:18:22,410
And then the final consideration that
we look at when grading is style.

399
00:18:22,410 --> 00:18:25,140
And style is less about
the efficiency of the code,

400
00:18:25,140 --> 00:18:27,120
and is more just about
how the code looks.

401
00:18:27,120 --> 00:18:31,710
Because, especially if students are
aspiring to become software engineers

402
00:18:31,710 --> 00:18:34,170
or working in computer
science in the future--

403
00:18:34,170 --> 00:18:37,920
writing code that is readable by other
people, whether it's by coworkers,

404
00:18:37,920 --> 00:18:41,550
or other people on the internet,
or even you as the educator,

405
00:18:41,550 --> 00:18:42,720
that's really important too.

406
00:18:42,720 --> 00:18:45,137
So that it's clear what you
mean when you're writing code.

407
00:18:45,137 --> 00:18:47,190
That it's easy to
follow and easy to read.

408
00:18:47,190 --> 00:18:51,800
And we want to encourage those
best style practices too.

409
00:18:51,800 --> 00:18:53,050
DAVID MALAN: Thank you, Brian.

410
00:18:53,050 --> 00:18:55,092
There was a question in
the chat about a project,

411
00:18:55,092 --> 00:18:57,550
but would be best to email
that to someone, something

412
00:18:57,550 --> 00:18:59,740
like certificates@cs50.harvard.edu.

413
00:18:59,740 --> 00:19:02,290
We can paste that email into the chat.

414
00:19:02,290 --> 00:19:05,200
Well, transitioning perhaps
to-- no, actually, one

415
00:19:05,200 --> 00:19:07,230
note on grading philosophy if I may.

416
00:19:07,230 --> 00:19:10,090
So here on campus, where we
have the luxury of having

417
00:19:10,090 --> 00:19:13,570
a reasonably manageable ratio between
teachers and students by nature

418
00:19:13,570 --> 00:19:16,660
of it being a traditional course
offering, here in a college environment

419
00:19:16,660 --> 00:19:18,220
where we have a number of TAs.

420
00:19:18,220 --> 00:19:21,310
And so, we're able to provide
feedback along each of these axis.

421
00:19:21,310 --> 00:19:25,210
Generally speaking our online students,
whether taking CS50 AP through edX,

422
00:19:25,210 --> 00:19:28,120
or CS50x, or any of the courses,
do indeed as Brian notes,

423
00:19:28,120 --> 00:19:32,710
rely on the automated correctness
tool, namely check50 in our case,

424
00:19:32,710 --> 00:19:34,120
to focus on correctness.

425
00:19:34,120 --> 00:19:37,000
Style too, to some extent,
we rely on style50--

426
00:19:37,000 --> 00:19:40,600
a linter tool that provides, indeed,
this sort of quantitative feedback

427
00:19:40,600 --> 00:19:41,740
as best it can.

428
00:19:41,740 --> 00:19:48,885
Design though, is really the
most labor intensive axis along

429
00:19:48,885 --> 00:19:50,260
which to evaluate students' work.

430
00:19:50,260 --> 00:19:52,150
And certainly teachers in
high school, if I think back

431
00:19:52,150 --> 00:19:53,620
when I had some 100 students.

432
00:19:53,620 --> 00:19:55,870
And I was getting homework
per week, and that was just

433
00:19:55,870 --> 00:19:57,730
in math not even in computer science.

434
00:19:57,730 --> 00:20:02,020
Is it pretty daunting to even imagine
going through and qualitatively

435
00:20:02,020 --> 00:20:03,412
providing feedback as well?

436
00:20:03,412 --> 00:20:06,370
So these are among the knobs that we
generally find that teachers turn.

437
00:20:06,370 --> 00:20:09,970
Focusing, for instance, generally on
only one, maybe two, of these axis,

438
00:20:09,970 --> 00:20:11,620
but not necessarily all three.

439
00:20:11,620 --> 00:20:14,980
Fortunately, with the trends being what
they are in artificial intelligence

440
00:20:14,980 --> 00:20:17,620
and machine learning, we're
hopeful that even design

441
00:20:17,620 --> 00:20:21,400
will be able to be automated to some
extent by computers before long.

442
00:20:21,400 --> 00:20:25,120
But at least within our ecosystem,
we're not quite there yet.

443
00:20:25,120 --> 00:20:27,850
But thought we would now
pivot to what we've described,

444
00:20:27,850 --> 00:20:31,090
and what most anyone would describe,
as memorable moments, hopefully.

445
00:20:31,090 --> 00:20:34,540
Particularly among students, seeing
what they see-- on our case on camera,

446
00:20:34,540 --> 00:20:36,910
but what you probably do most
any day in the classroom,

447
00:20:36,910 --> 00:20:39,230
any time you try to
bring some topic to life.

448
00:20:39,230 --> 00:20:41,920
And we thought we would give
just a few examples of some

449
00:20:41,920 --> 00:20:47,500
of the visuals, some of the theatrics
that we try to integrate into CS50

450
00:20:47,500 --> 00:20:48,730
here itself.

451
00:20:48,730 --> 00:20:53,620
And, by way of a few photos,
might you recognize this?

452
00:20:53,620 --> 00:20:56,240
These are getting harder and
harder to find, honestly.

453
00:20:56,240 --> 00:20:59,470
But if you ever want to do a
demonstration of binary search,

454
00:20:59,470 --> 00:21:03,880
or divide and conquer more generally, or
really problem solving most generally--

455
00:21:03,880 --> 00:21:06,970
I definitely recommend keeping an
eye out for these in the mail room

456
00:21:06,970 --> 00:21:10,090
or on someone's shelf who clearly
doesn't need that phone book anymore.

457
00:21:10,090 --> 00:21:13,630
And to use this, as perhaps
one of the earliest visuals

458
00:21:13,630 --> 00:21:14,710
to present to students.

459
00:21:14,710 --> 00:21:19,570
And nowadays, I think it's probably
important to link this physical device

460
00:21:19,570 --> 00:21:22,870
to the Virtual Contacts app
in everyone's Android device

461
00:21:22,870 --> 00:21:23,860
or iPhone device.

462
00:21:23,860 --> 00:21:25,430
But it really is the same problem.

463
00:21:25,430 --> 00:21:27,790
So even though this is the
old school incarnation of it,

464
00:21:27,790 --> 00:21:30,730
this ripping of the phone
book at the beginning of CS50,

465
00:21:30,730 --> 00:21:33,490
which probably is not
something students often see,

466
00:21:33,490 --> 00:21:36,970
is one of the memorable
moments that we try to create.

467
00:21:36,970 --> 00:21:41,170
So that even as we get into the weeds
of these fairly arcane topics, very

468
00:21:41,170 --> 00:21:45,010
unfamiliar topics for many
students, they can latch onto, "OK,

469
00:21:45,010 --> 00:21:46,000
binary search.

470
00:21:46,000 --> 00:21:47,200
Oh, phone book."

471
00:21:47,200 --> 00:21:50,740
And they at least have those visuals
that can help remind them of the topic.

472
00:21:50,740 --> 00:21:54,040
And at least help them find that
same material in their mind's

473
00:21:54,040 --> 00:21:56,890
eye or, say, on the course's website.

474
00:21:56,890 --> 00:22:00,455
Brian, this next one
here is representative

475
00:22:00,455 --> 00:22:02,080
of a general problem solving technique.

476
00:22:02,080 --> 00:22:06,460
Do you want to speak to why we
put this black box on the stage?

477
00:22:06,460 --> 00:22:10,420
BRIAN YU: So we use the black box to
introduce a topic in computer science

478
00:22:10,420 --> 00:22:12,610
that's commonly known as abstraction.

479
00:22:12,610 --> 00:22:16,130
And having worked with CS50
students year after year,

480
00:22:16,130 --> 00:22:19,720
this is one of the trickiest topics for
students to really understand at first.

481
00:22:19,720 --> 00:22:22,060
What does abstraction mean?

482
00:22:22,060 --> 00:22:24,038
And one of the ways
that we try to frame it,

483
00:22:24,038 --> 00:22:26,830
and there are lots of different
ways of trying to frame abstraction

484
00:22:26,830 --> 00:22:30,460
and what it's all
about, is in recognizing

485
00:22:30,460 --> 00:22:34,750
that dealing with all of the details
of every part of a computer program

486
00:22:34,750 --> 00:22:39,050
might get extremely complex
and difficult to reason about.

487
00:22:39,050 --> 00:22:41,980
But if you can start to think about
things as more of a black box,

488
00:22:41,980 --> 00:22:44,710
you provide input into
some part of the program,

489
00:22:44,710 --> 00:22:47,050
and that black box might
produce some output.

490
00:22:47,050 --> 00:22:50,630
Then thinking about those
components of the program,

491
00:22:50,630 --> 00:22:54,310
even if you don't understand everything
going on inside of that black box,

492
00:22:54,310 --> 00:22:57,280
can help you to build bigger
pieces together and construct

493
00:22:57,280 --> 00:22:59,170
more interesting programs.

494
00:22:59,170 --> 00:23:02,320
And that's a tricky concept to
understand and code at first.

495
00:23:02,320 --> 00:23:05,530
And we hope that the black box
visual is a bit of a metaphor

496
00:23:05,530 --> 00:23:08,388
that students can use for thinking
about that type of thing too.

497
00:23:08,388 --> 00:23:11,430
DAVID MALAN: Brian, let me pluck off
a couple of questions from the chat.

498
00:23:11,430 --> 00:23:15,560
Can CS50x students have access
to sections as recorded in video?

499
00:23:15,560 --> 00:23:17,580
So this is actually
one of the reasons too,

500
00:23:17,580 --> 00:23:19,950
why we provide the shorts,
as well as most recently,

501
00:23:19,950 --> 00:23:23,490
the videos within the labs that
were introduced this past year.

502
00:23:23,490 --> 00:23:26,940
Because those sections are generally
more discussion oriented, and not high

503
00:23:26,940 --> 00:23:28,780
information content for the viewer.

504
00:23:28,780 --> 00:23:31,500
And so, those two alternative exists.

505
00:23:31,500 --> 00:23:34,753
Stephen notes that his Zoomer students
don't know what a phone book is.

506
00:23:34,753 --> 00:23:37,170
Indeed, this is the reality
that we're bumping up against,

507
00:23:37,170 --> 00:23:39,450
and the mod proposes using
a hardcover dictionary.

508
00:23:39,450 --> 00:23:42,330
I've not been able to get
myself to get comfortable

509
00:23:42,330 --> 00:23:45,720
with the idea of tearing
actual books really meant to,

510
00:23:45,720 --> 00:23:48,120
or destined to be recycled anyway.

511
00:23:48,120 --> 00:23:51,450
So I would, perhaps, beware
tearing in half something that

512
00:23:51,450 --> 00:23:56,010
might have more impact
than something discardable,

513
00:23:56,010 --> 00:23:58,150
annually, like a dictionary.

514
00:23:58,150 --> 00:24:01,770
So this is one that took a colleague
of ours some time to build.

515
00:24:01,770 --> 00:24:03,780
And it doesn't need to
be this sophisticated,

516
00:24:03,780 --> 00:24:05,940
and indeed, you're about
to see a few photos that

517
00:24:05,940 --> 00:24:08,190
are the result of our
having collaborated

518
00:24:08,190 --> 00:24:12,210
this past year with a
wonderfully talented prop shop

519
00:24:12,210 --> 00:24:14,160
as well as colleagues across campus.

520
00:24:14,160 --> 00:24:16,410
Where we've had the resources
and some of the hardware

521
00:24:16,410 --> 00:24:18,450
around with which to build
some of these things.

522
00:24:18,450 --> 00:24:20,790
But all of these are born
of much simpler ideas.

523
00:24:20,790 --> 00:24:24,360
Before we had some metal and eight
light bulbs and electricity like this,

524
00:24:24,360 --> 00:24:26,453
I would just have a few
students, three students,

525
00:24:26,453 --> 00:24:29,370
eight students come to the front of
the room and hold up their phones,

526
00:24:29,370 --> 00:24:31,230
which generally have
flashlights these days.

527
00:24:31,230 --> 00:24:33,720
Or I picked up a few desk
lamps for a few dollars

528
00:24:33,720 --> 00:24:35,820
at Target, a local retail store.

529
00:24:35,820 --> 00:24:38,820
So as to represent what we've
called here, binary bulbs.

530
00:24:38,820 --> 00:24:42,960
Light bulbs that represent bits or
transistors being turned on and off.

531
00:24:42,960 --> 00:24:46,410
And metaphorically being the light bulb,
we hope, goes off in students' head

532
00:24:46,410 --> 00:24:47,770
very early in the semester.

533
00:24:47,770 --> 00:24:51,210
And if you've not seen this one
before, these are magnetic numbers

534
00:24:51,210 --> 00:24:53,850
that a child might play with
on the refrigerator, that

535
00:24:53,850 --> 00:24:56,820
just represent what place each
of these light bulbs represents.

536
00:24:56,820 --> 00:25:00,240
The lowest ordered bit on the right,
and the highest order bit on the left.

537
00:25:00,240 --> 00:25:04,275
We use this to just have some
visual fun talking about binary.

538
00:25:04,275 --> 00:25:06,390
It used turning switches
on and off here,

539
00:25:06,390 --> 00:25:08,460
but again, any light bulb suffices.

540
00:25:08,460 --> 00:25:10,650
And then we dramatically,
because of the magnets,

541
00:25:10,650 --> 00:25:14,100
have a second student come up
typically during this demonstration.

542
00:25:14,100 --> 00:25:17,910
And I then try to dramatically wipe
off all of the magnetic letters,

543
00:25:17,910 --> 00:25:19,290
such that they fall on the floor.

544
00:25:19,290 --> 00:25:22,230
And so now, it's like
Luke Skywalker mode,

545
00:25:22,230 --> 00:25:26,740
trying to visualize only in their
mind's eye what each place represents,

546
00:25:26,740 --> 00:25:28,350
so as to ramp things up.

547
00:25:28,350 --> 00:25:31,860
But here too, even though we might
end up spending a few extra minutes

548
00:25:31,860 --> 00:25:35,040
on a demonstration like this, it's
a lot more interesting certainly

549
00:25:35,040 --> 00:25:37,080
than going to a
chalkboard or a whiteboard

550
00:25:37,080 --> 00:25:39,900
and just jotting down
patterns of zeros and ones.

551
00:25:39,900 --> 00:25:43,560
Again, trying to bring the topic to
life is the goal of a visual like this.

552
00:25:43,560 --> 00:25:48,120
Whether it's complicated as this build,
or as simple as just having students

553
00:25:48,120 --> 00:25:52,200
use their own phones and flashlights.

554
00:25:52,200 --> 00:25:56,580
So this is a larger duck than you
might have on your desk at home.

555
00:25:56,580 --> 00:25:58,420
And this is deliberately
meant to be, again,

556
00:25:58,420 --> 00:26:02,040
another dramatic visual that is
actually incarnated in smaller form.

557
00:26:02,040 --> 00:26:05,460
But Brian, do you want to speak to
why there's such a big duck here,

558
00:26:05,460 --> 00:26:08,700
or rather a smaller duck that
we tend to hand out to students

559
00:26:08,700 --> 00:26:10,837
back in healthier times here on campus?

560
00:26:10,837 --> 00:26:12,420
BRIAN YU: This is one of my favorites.

561
00:26:12,420 --> 00:26:14,400
This little thing is a duck debugger.

562
00:26:14,400 --> 00:26:17,040
And one of the most common
things you have to teach students

563
00:26:17,040 --> 00:26:19,040
when they're first working
with computer science

564
00:26:19,040 --> 00:26:20,400
is, how do you debug their code?

565
00:26:20,400 --> 00:26:23,040
Odds are, their programs
won't work on the first try.

566
00:26:23,040 --> 00:26:25,290
And there are all sorts of
techniques for debugging.

567
00:26:25,290 --> 00:26:27,510
Adding print statements
to see what's going on,

568
00:26:27,510 --> 00:26:30,060
we teach students how to use
a graphical debugger where

569
00:26:30,060 --> 00:26:31,980
they can step through
their code line by line

570
00:26:31,980 --> 00:26:33,900
and look at the values of variables.

571
00:26:33,900 --> 00:26:37,710
But maybe one of the simplest is just
using one of these little rubber ducks

572
00:26:37,710 --> 00:26:40,170
and using a technique known
as "rubber duck debugging".

573
00:26:40,170 --> 00:26:42,480
Where the student just
talks to the duck,

574
00:26:42,480 --> 00:26:45,460
and explains to the duck,
what their code is doing

575
00:26:45,460 --> 00:26:47,460
and what they're trying
to get their code to do.

576
00:26:47,460 --> 00:26:50,520
And amazingly, even though I
wouldn't have thought so at first,

577
00:26:50,520 --> 00:26:54,210
just talking through the problem
to the duck is often enough for you

578
00:26:54,210 --> 00:26:57,120
to realize, "Oh, this is
exactly what my mistake is."

579
00:26:57,120 --> 00:26:59,730
The act of articulating
the problem trying

580
00:26:59,730 --> 00:27:03,817
to explain it from first principles
helps you to realize what's gone wrong.

581
00:27:03,817 --> 00:27:06,150
And ultimately, eventually
you don't even need the duck.

582
00:27:06,150 --> 00:27:08,610
But especially when you're
starting out, just having something

583
00:27:08,610 --> 00:27:10,560
there as a reminder of
something you can talk

584
00:27:10,560 --> 00:27:12,660
to as you're working
through your problems

585
00:27:12,660 --> 00:27:14,520
can definitely be quite helpful.

586
00:27:14,520 --> 00:27:18,240
And even in CS50 IDE,
the online code editor

587
00:27:18,240 --> 00:27:20,670
that we have students
use in CS50, there's

588
00:27:20,670 --> 00:27:23,760
a little virtual rubber duck
in the upper right hand corner.

589
00:27:23,760 --> 00:27:26,760
So that students can use that as a
debugging technique, if they'd like

590
00:27:26,760 --> 00:27:29,265
to try working on debugging their code.

591
00:27:29,265 --> 00:27:31,890
DAVID MALAN: And this is the sort
of thing that, it's not free.

592
00:27:31,890 --> 00:27:34,260
And we actually stamp our
own name CS50 on the rubber

593
00:27:34,260 --> 00:27:35,430
ducks that we find online.

594
00:27:35,430 --> 00:27:39,030
But I'm actually in a few teacher
Facebook groups, where every year

595
00:27:39,030 --> 00:27:41,220
it's fun to see teachers
posting online some deal

596
00:27:41,220 --> 00:27:43,410
they found on Amazon for
just a few cents each.

597
00:27:43,410 --> 00:27:45,810
Getting a whole bunch,
like a bag of these rubber

598
00:27:45,810 --> 00:27:47,830
ducks on sale to present
to their students.

599
00:27:47,830 --> 00:27:52,290
So if resources permit, it's a fun way
to, again, bring to life some topic

600
00:27:52,290 --> 00:27:55,530
and also genuinely empower
students with a technique that

601
00:27:55,530 --> 00:27:56,810
might very well help them.

602
00:27:56,810 --> 00:27:58,560
And frankly, it doesn't
need to be a duck.

603
00:27:58,560 --> 00:27:59,730
It can be anything at all.

604
00:27:59,730 --> 00:28:02,110
It can be a picture of a duck
that they draw themselves.

605
00:28:02,110 --> 00:28:04,818
So even there, too, there's a
range of possibilities that doesn't

606
00:28:04,818 --> 00:28:08,110
need to be a physical thing as well.

607
00:28:08,110 --> 00:28:13,510
So here, this has been a dream of mine
for 15+ years to actually talk about

608
00:28:13,510 --> 00:28:14,230
binary search.

609
00:28:14,230 --> 00:28:17,350
Not just with the phone
book, but with actual doors.

610
00:28:17,350 --> 00:28:19,970
Since I've long envisioned
this idea, this theatricality

611
00:28:19,970 --> 00:28:22,720
of being able to walk in front of
a bunch of doors, open the door,

612
00:28:22,720 --> 00:28:25,630
and look behind it to see
what number is hidden there.

613
00:28:25,630 --> 00:28:29,350
Toward an end of introducing students to
the problem, more generally, of search.

614
00:28:29,350 --> 00:28:31,930
For instance, searching
an array of numbers,

615
00:28:31,930 --> 00:28:35,750
and array being applicable to our
focus on C early on in the semester.

616
00:28:35,750 --> 00:28:38,140
And by nature of COVID this
past year, unfortunately,

617
00:28:38,140 --> 00:28:41,350
not only was most everything shut
down, so was one of the local theaters

618
00:28:41,350 --> 00:28:42,490
here in Cambridge.

619
00:28:42,490 --> 00:28:45,820
As the result of which was, that
we did have this rare opportunity

620
00:28:45,820 --> 00:28:47,920
to collaborate with their own prop shop.

621
00:28:47,920 --> 00:28:52,330
And so, what you're seeing here is
a photograph of eight or so doors

622
00:28:52,330 --> 00:28:54,760
that were just in storage
at the back of the theater

623
00:28:54,760 --> 00:28:58,070
that they were able to bring
back to the front of the stage.

624
00:28:58,070 --> 00:28:59,870
So as to do a demonstration like this.

625
00:28:59,870 --> 00:29:02,980
And this is not one that, generally,
we can do here in healthy times.

626
00:29:02,980 --> 00:29:07,180
Most of us probably don't have access to
eight full fledged, human sized doors.

627
00:29:07,180 --> 00:29:11,200
However, those of you who are in high
schools or middle schools probably

628
00:29:11,200 --> 00:29:15,680
have a hallway full of lockers or a
gymnasium that has something like that.

629
00:29:15,680 --> 00:29:18,040
And so, what we've also
done in other times

630
00:29:18,040 --> 00:29:21,310
is actually get a few metal
lockers, either on campus

631
00:29:21,310 --> 00:29:23,350
or bring them into
the space temporarily.

632
00:29:23,350 --> 00:29:25,930
And being able to use that
physical demonstration is

633
00:29:25,930 --> 00:29:28,480
nice in that, when
talking about arrays, when

634
00:29:28,480 --> 00:29:32,560
talking about searching behind
those arrays, the fact that there

635
00:29:32,560 --> 00:29:34,240
is this physical door--

636
00:29:34,240 --> 00:29:36,910
especially in the world of
C or really any language,

637
00:29:36,910 --> 00:29:40,810
Java included, that supports
arrays, makes all the clearer

638
00:29:40,810 --> 00:29:45,063
that a computer can really only look
at one of these values at a time.

639
00:29:45,063 --> 00:29:47,980
The problem, of course, being if you
just put a whole bunch of numbers

640
00:29:47,980 --> 00:29:50,140
on the stage or in the
front of the classroom,

641
00:29:50,140 --> 00:29:53,380
yes, you can say to students
that they should only

642
00:29:53,380 --> 00:29:57,400
look at one number at a time when
searching for a particular value.

643
00:29:57,400 --> 00:30:00,890
But as humans, we all probably take in
everything we're seeing all at once,

644
00:30:00,890 --> 00:30:02,890
and boom, there's the
number you're looking for.

645
00:30:02,890 --> 00:30:04,240
Or boom, it's over there.

646
00:30:04,240 --> 00:30:06,220
There's not necessarily
the opportunity to do

647
00:30:06,220 --> 00:30:08,440
the mechanics of searching
from left to right,

648
00:30:08,440 --> 00:30:11,870
or from right to left, or even
binary search in the middle on down.

649
00:30:11,870 --> 00:30:15,290
So using something that physically
closes like doors in this one case,

650
00:30:15,290 --> 00:30:17,660
and sadly we won't have
access to these anymore.

651
00:30:17,660 --> 00:30:20,770
But-- or lockers, or even
paper cups, or something

652
00:30:20,770 --> 00:30:23,470
which you can use to hide
something there or not,

653
00:30:23,470 --> 00:30:28,030
we found to be of another very effective
visual for students to latch on to.

654
00:30:28,030 --> 00:30:31,300
Brian, meanwhile, did have an
opportunity to use some actual numbers.

655
00:30:31,300 --> 00:30:34,282
This time, we didn't
use the doors because we

656
00:30:34,282 --> 00:30:36,490
thought it would be way too
much opening and closing.

657
00:30:36,490 --> 00:30:38,530
And at this point, we
wanted to talk to students

658
00:30:38,530 --> 00:30:42,620
about sorting those very same numbers.

659
00:30:42,620 --> 00:30:45,370
And if you're given a bunch of
numbers like these in random order,

660
00:30:45,370 --> 00:30:48,520
these happen to be plastic numbers
that we found on Amazon, they even

661
00:30:48,520 --> 00:30:51,702
have little light bulbs if you put in
a tiny battery that turn on and off.

662
00:30:51,702 --> 00:30:53,410
But we just wanted
some physical numbers.

663
00:30:53,410 --> 00:30:55,280
And in the past, we've done
this with sheets of paper,

664
00:30:55,280 --> 00:30:56,980
where we just write the
numbers on the board.

665
00:30:56,980 --> 00:30:59,272
Here we wanted to try something
a little more physical.

666
00:30:59,272 --> 00:31:03,170
And Brian, do you to explain
what you did with these numbers?

667
00:31:03,170 --> 00:31:05,170
BRIAN YU: So the idea of
using these numbers was

668
00:31:05,170 --> 00:31:08,800
to visualize what it looks like to
perform a sorting algorithm, something

669
00:31:08,800 --> 00:31:12,260
like bubble sort, or
selections for example.

670
00:31:12,260 --> 00:31:15,460
And the nice thing about using
physical numbers on a shelf

671
00:31:15,460 --> 00:31:18,970
is that it reminds students of a
couple of important properties of what

672
00:31:18,970 --> 00:31:21,280
it's really like to sort
numbers in an array.

673
00:31:21,280 --> 00:31:23,965
One being, that there's not a
whole lot of shelf space here.

674
00:31:23,965 --> 00:31:25,840
So it wouldn't be that
easy to take a number,

675
00:31:25,840 --> 00:31:29,810
and squeeze it in between two other
numbers without making the space tight.

676
00:31:29,810 --> 00:31:33,370
So if you want to move numbers around,
you really need to take one number,

677
00:31:33,370 --> 00:31:35,620
remove it from its place,
take another number,

678
00:31:35,620 --> 00:31:39,570
and put it there, for example, to really
emphasize that each of these numbers

679
00:31:39,570 --> 00:31:42,280
is in some particular
spot inside of an array.

680
00:31:42,280 --> 00:31:45,730
And you can remove something from it, in
order to make room for something else.

681
00:31:45,730 --> 00:31:49,035
And the other nice property
is that these numbers are,

682
00:31:49,035 --> 00:31:51,160
you have to hold them in
order to move them around.

683
00:31:51,160 --> 00:31:54,280
And it's not easy for me, just to
pick up all eight of the numbers,

684
00:31:54,280 --> 00:31:56,030
and then put them exactly where I want.

685
00:31:56,030 --> 00:32:00,950
I can really only be working with one
or maybe two numbers at any given time.

686
00:32:00,950 --> 00:32:02,800
Which is a good reminder
to students as well

687
00:32:02,800 --> 00:32:05,230
that the program can
really be working with--

688
00:32:05,230 --> 00:32:07,820
your program is doing one
thing at any given time.

689
00:32:07,820 --> 00:32:10,960
And it's taking a variable,
putting some value inside of it,

690
00:32:10,960 --> 00:32:13,550
swapping some value or
something like that.

691
00:32:13,550 --> 00:32:15,610
And so, this offers a
good way of visualizing

692
00:32:15,610 --> 00:32:18,680
what these algorithms look like,
seeing them a little bit more slowly,

693
00:32:18,680 --> 00:32:19,910
step by step.

694
00:32:19,910 --> 00:32:22,210
And I think it's helpful
for understanding

695
00:32:22,210 --> 00:32:24,178
how it is that these algorithms work.

696
00:32:24,178 --> 00:32:26,220
DAVID MALAN: For those
who missed it in the chat,

697
00:32:26,220 --> 00:32:29,460
shoe boxes were proposed too,
as a mechanism for hiding

698
00:32:29,460 --> 00:32:30,810
some value that might be inside.

699
00:32:30,810 --> 00:32:32,440
I like that one as well.

700
00:32:32,440 --> 00:32:34,650
Now in healthier times,
this is a photograph

701
00:32:34,650 --> 00:32:37,260
of some students we actually
had come up on stage.

702
00:32:37,260 --> 00:32:39,730
Brian was doing that in
isolation this past year.

703
00:32:39,730 --> 00:32:41,820
But when we have the
opportunity to have students

704
00:32:41,820 --> 00:32:44,460
come to the front of the class,
we have in some semesters just

705
00:32:44,460 --> 00:32:45,918
handed them those physical numbers.

706
00:32:45,918 --> 00:32:49,470
Either the plastic numbers here, or
just print outs in very bold fonts.

707
00:32:49,470 --> 00:32:54,360
So that it's clear to the
students sitting down,

708
00:32:54,360 --> 00:32:56,280
what numbers the students are holding.

709
00:32:56,280 --> 00:33:00,150
And here too, it's a nice visual
in that there's a lot of movement.

710
00:33:00,150 --> 00:33:04,170
And the fact that it is so expensive
to keep walking back and forth,

711
00:33:04,170 --> 00:33:06,360
moving these numbers
around, rather sets in.

712
00:33:06,360 --> 00:33:09,008
The downside of using
humans and students

713
00:33:09,008 --> 00:33:10,800
for these kinds of
demonstrations, this is,

714
00:33:10,800 --> 00:33:13,690
that I do think it's also a
little harder for the audience.

715
00:33:13,690 --> 00:33:17,730
Especially if they're not 100% following
along with this new topic, like bubble

716
00:33:17,730 --> 00:33:21,990
sort, or selection, or the like
to understand what's going on,

717
00:33:21,990 --> 00:33:23,530
because it's a little sloppy.

718
00:33:23,530 --> 00:33:27,540
And so, I would keep that in mind any
time you do use human participants.

719
00:33:27,540 --> 00:33:30,490
And that the demonstration might
not very well go according to plan.

720
00:33:30,490 --> 00:33:33,720
And that's fine too, if it's just
meant to be a memorable moment that you

721
00:33:33,720 --> 00:33:35,665
can then come back to again and again.

722
00:33:35,665 --> 00:33:38,790
But there's something to be said too,
I think, for the cleanliness of doing

723
00:33:38,790 --> 00:33:41,320
it yourself, or as Brian did it, alone.

724
00:33:41,320 --> 00:33:44,920
So that you can really choreograph
things and get it just right.

725
00:33:44,920 --> 00:33:48,510
But there's perhaps a nice
balance between those two.

726
00:33:48,510 --> 00:33:50,640
Some of you might have
seen the videos online of,

727
00:33:50,640 --> 00:33:54,150
I think it's a Hungarian dance group
does something for bubble sort,

728
00:33:54,150 --> 00:33:56,340
and selection sort, and
insertion sort and others.

729
00:33:56,340 --> 00:33:58,950
And those are fun too, but
they're rather for the viewer

730
00:33:58,950 --> 00:34:00,600
that already knows what's going on.

731
00:34:00,600 --> 00:34:02,517
Because there's a lot
more spinning than there

732
00:34:02,517 --> 00:34:06,220
needs to be, for instance, in
a typical sorting algorithm.

733
00:34:06,220 --> 00:34:08,670
So this is a fun one that
can happen very early

734
00:34:08,670 --> 00:34:12,630
on in the semester, whether using C
or any language, when it comes time

735
00:34:12,630 --> 00:34:16,020
to just talk about variables, and
assigning values to variables,

736
00:34:16,020 --> 00:34:17,460
and swapping values.

737
00:34:17,460 --> 00:34:19,830
And we introduced this
a few weeks in, if only

738
00:34:19,830 --> 00:34:23,060
because a lot of these
algorithms we just talked about--

739
00:34:23,060 --> 00:34:24,810
selection sort, bubble
sort, and the like,

740
00:34:24,810 --> 00:34:28,830
generally involves swapping the
locations of two things in memory.

741
00:34:28,830 --> 00:34:32,010
Now in Python, you can do
this with one line of code

742
00:34:32,010 --> 00:34:33,900
that just magically swaps two things.

743
00:34:33,900 --> 00:34:37,679
In most languages, you need to be a
little more pedantic unless you resort

744
00:34:37,679 --> 00:34:39,670
to bitwise operators and the like.

745
00:34:39,670 --> 00:34:42,179
And you need generally
a temporary variable.

746
00:34:42,179 --> 00:34:46,560
And so, Brian, when you did this,
this year, what was your goal?

747
00:34:46,560 --> 00:34:50,190
BRIAN YU: So the question we asked
the students is, how would you change

748
00:34:50,190 --> 00:34:52,020
which glass contains which liquid?

749
00:34:52,020 --> 00:34:55,090
Like get the glass on the left to
contain the blue liquid instead.

750
00:34:55,090 --> 00:34:58,140
And get the glass on the right
to contain the red liquid.

751
00:34:58,140 --> 00:35:02,370
And most of the students were
able to pretty quickly come up

752
00:35:02,370 --> 00:35:05,250
with the realization that if
you just have these two glasses,

753
00:35:05,250 --> 00:35:06,750
you can't quite do that.

754
00:35:06,750 --> 00:35:08,910
And that the solution
is to use a third glass.

755
00:35:08,910 --> 00:35:12,600
You pour the red liquid maybe
into the third empty glass.

756
00:35:12,600 --> 00:35:15,240
And now, you have room
to take the blue liquid,

757
00:35:15,240 --> 00:35:17,760
put it into the glass that
used to hold the red liquid,

758
00:35:17,760 --> 00:35:21,910
and then transfer the red liquid
into the new glass as well.

759
00:35:21,910 --> 00:35:25,140
And this is always a great demonstration
because if you just gave students

760
00:35:25,140 --> 00:35:28,020
two variables, an integer
called X and an integer

761
00:35:28,020 --> 00:35:32,220
called Y, and told them to swap
them, most won't immediately

762
00:35:32,220 --> 00:35:34,530
come up with exactly what
the right lines of code

763
00:35:34,530 --> 00:35:36,720
are to perform that swapping procedure.

764
00:35:36,720 --> 00:35:39,150
But introducing this
demo first, most students

765
00:35:39,150 --> 00:35:42,630
figure out the logic very quickly of
being able to see the actual liquid,

766
00:35:42,630 --> 00:35:46,170
seeing how they need to be poured into
other glasses to get them to swap,

767
00:35:46,170 --> 00:35:49,480
and then you can translate that
back into what the original C

768
00:35:49,480 --> 00:35:50,407
code looks like.

769
00:35:50,407 --> 00:35:52,740
DAVID MALAN: And when it's
an actual student doing this,

770
00:35:52,740 --> 00:35:55,020
I mean, we deliberately
only give them two glasses.

771
00:35:55,020 --> 00:35:56,790
We ask them to swap the two values.

772
00:35:56,790 --> 00:35:59,400
And then, there's the
sort of awkward moment

773
00:35:59,400 --> 00:36:02,797
where they realize this is not really
going to be easy or even possible.

774
00:36:02,797 --> 00:36:05,130
At which point, you can whip
out the temporary variable,

775
00:36:05,130 --> 00:36:06,990
the third glass in the story.

776
00:36:06,990 --> 00:36:10,350
When it's, for instance, the student
and not just the teacher or Brian.

777
00:36:10,350 --> 00:36:13,290
Just to now give you a taste
of some of the other visuals

778
00:36:13,290 --> 00:36:14,520
we've used in recent years.

779
00:36:14,520 --> 00:36:17,970
We found an old spare mailbox
that we've used as a metaphor

780
00:36:17,970 --> 00:36:22,230
to talk about addresses in the context
of C, and how every location in memory

781
00:36:22,230 --> 00:36:24,180
indeed has an address of some sort.

782
00:36:24,180 --> 00:36:27,030
We use this as an opportunity to
talk briefly about hexadecimal,

783
00:36:27,030 --> 00:36:28,815
if only because they're
going to see zero

784
00:36:28,815 --> 00:36:33,900
X dot dot dot in a bunch of context like
the debugger, or perhaps other tools.

785
00:36:33,900 --> 00:36:34,983
And that's a fun metaphor.

786
00:36:34,983 --> 00:36:37,983
And even if this isn't something to
bring to the front of the classroom,

787
00:36:37,983 --> 00:36:40,680
you could imagine doing a little
skit on video, even in advance,

788
00:36:40,680 --> 00:36:44,220
using one's own neighborhood
and mailboxes along the street.

789
00:36:44,220 --> 00:36:46,470
We do use a dictionary toward
the end of the semester.

790
00:36:46,470 --> 00:36:51,180
Not for the tearing example, but to talk
about dictionaries with key value pairs

791
00:36:51,180 --> 00:36:53,790
and hash tables underneath the hood.

792
00:36:53,790 --> 00:36:56,580
And this, honestly, doesn't serve
much more function other than,

793
00:36:56,580 --> 00:36:58,295
"hey all, here's a dictionary."

794
00:36:58,295 --> 00:36:59,670
This is what we're talking about.

795
00:36:59,670 --> 00:37:04,050
Just again, to put a visual on the
stage or in the front of the classroom

796
00:37:04,050 --> 00:37:06,180
so that students again
have like a visual

797
00:37:06,180 --> 00:37:11,280
to latch onto when thinking about or
revisiting an otherwise arcane topic.

798
00:37:11,280 --> 00:37:15,450
This, too, was a side effect of
having access to a whole prop shop.

799
00:37:15,450 --> 00:37:18,755
We, for the first time in 15 years,
had access to an actual refrigerator

800
00:37:18,755 --> 00:37:21,130
that we were able to bring
out to the front of the class.

801
00:37:21,130 --> 00:37:24,990
And we use this to talk about
locking and race conditions

802
00:37:24,990 --> 00:37:26,220
in the context of SQL.

803
00:37:26,220 --> 00:37:29,580
Long story, short, there are
certain challenges in computing

804
00:37:29,580 --> 00:37:32,220
whenever you have multiple
threads or multiple users trying

805
00:37:32,220 --> 00:37:34,348
to do things at roughly the same time.

806
00:37:34,348 --> 00:37:37,140
Bad things can happen if two
different users, two different threads

807
00:37:37,140 --> 00:37:39,010
are trying to access the same value.

808
00:37:39,010 --> 00:37:41,760
And the way I learned about
race conditions back in the day

809
00:37:41,760 --> 00:37:44,550
is in the context of a
refrigerator and opening it

810
00:37:44,550 --> 00:37:49,000
up, checking to see if you
have some milk in the fridge.

811
00:37:49,000 --> 00:37:52,290
And if not, you walk off to the
store, and you go and buy some milk.

812
00:37:52,290 --> 00:37:55,290
But problem arises if another
family member or roommate

813
00:37:55,290 --> 00:37:59,730
follows you and opens the door after
you've left, sees that there's no milk,

814
00:37:59,730 --> 00:38:01,645
and then tries to go
to the store as well.

815
00:38:01,645 --> 00:38:03,520
And then, you end up
with twice as much milk.

816
00:38:03,520 --> 00:38:06,810
So in this case, we actually, and you
can just see it on the floor there.

817
00:38:06,810 --> 00:38:10,590
We actually locked the thing
physically with the padlock and a chain

818
00:38:10,590 --> 00:38:15,820
just to bring to life that very low
level topic for students as well.

819
00:38:15,820 --> 00:38:19,920
This could certainly be achieved
with a camera in your own kitchen,

820
00:38:19,920 --> 00:38:21,660
just to make that same point.

821
00:38:21,660 --> 00:38:23,010
We talk about cookies.

822
00:38:23,010 --> 00:38:26,200
This is just an excuse to have cookies
for the team toward the end of class

823
00:38:26,200 --> 00:38:26,700
here.

824
00:38:26,700 --> 00:38:30,540
But when talking about cookies in the
context of HTTP and a shopping cart,

825
00:38:30,540 --> 00:38:32,460
turns out if you have
a local theater, they

826
00:38:32,460 --> 00:38:35,700
might very well have an old shopping
cart that we used to talk about state.

827
00:38:35,700 --> 00:38:37,950
And to talk about how
cookies can be used

828
00:38:37,950 --> 00:38:41,280
to create the illusion of
sessions, the maintenance of state

829
00:38:41,280 --> 00:38:44,590
across an otherwise
stateless protocol like HTTP.

830
00:38:44,590 --> 00:38:47,640
So again, just another memorable
moment that we tried to create.

831
00:38:47,640 --> 00:38:50,640
And then this one too, is meant to
be, this happens to be an old phone

832
00:38:50,640 --> 00:38:53,400
but you could do it with any
phone in the context of JavaScript

833
00:38:53,400 --> 00:38:55,680
asynchronous functions and callbacks.

834
00:38:55,680 --> 00:38:57,630
Whereby you call the
function, and you want

835
00:38:57,630 --> 00:39:01,278
it to call another function when it
has your return value essentially.

836
00:39:01,278 --> 00:39:04,320
Brian and I have started doing a little
skit in the past couple of years.

837
00:39:04,320 --> 00:39:08,317
Where I call him on stage,
and then I ask him a question

838
00:39:08,317 --> 00:39:10,650
that he needs a little bit
of time to get the answer to.

839
00:39:10,650 --> 00:39:14,440
So we hang up, I continue the class,
and then a few seconds, minutes later,

840
00:39:14,440 --> 00:39:16,980
the phone rings with my callback.

841
00:39:16,980 --> 00:39:19,433
At which point, he has
the answer to my question.

842
00:39:19,433 --> 00:39:21,600
So a fun little skit too,
that can be done certainly

843
00:39:21,600 --> 00:39:25,560
with a couple of cell
phones in one's pockets.

844
00:39:25,560 --> 00:39:29,340
SPEAKER 1: In this pandemic,
where we have to work from home

845
00:39:29,340 --> 00:39:35,910
and teach for home, have you used
some digital tools to substitute

846
00:39:35,910 --> 00:39:37,830
to this physical one?

847
00:39:37,830 --> 00:39:41,073
To exemplify that your show?

848
00:39:41,073 --> 00:39:42,490
DAVID MALAN: It's a good question.

849
00:39:42,490 --> 00:39:43,620
I did not.

850
00:39:43,620 --> 00:39:47,940
I had the fortune to be able to
continue teaching on campus this fall.

851
00:39:47,940 --> 00:39:50,700
No students were here, but we
were in fact in this space.

852
00:39:50,700 --> 00:39:53,670
But let me invite the group, if
most everyone here was indeed

853
00:39:53,670 --> 00:39:56,010
teaching online or hybrid
in some form this year,

854
00:39:56,010 --> 00:39:58,710
please do feel free to
volunteer via the chat--

855
00:39:58,710 --> 00:40:01,740
inspirations you might have had
using your own refrigerator,

856
00:40:01,740 --> 00:40:05,160
or glasses in the cupboard,
or anything along those lines.

857
00:40:05,160 --> 00:40:09,210
Since all of us did have to
get creative in some form.

858
00:40:09,210 --> 00:40:11,100
And now, as for the
course's problem sets.

859
00:40:11,100 --> 00:40:12,900
Wanted to touch on a
couple of final notes

860
00:40:12,900 --> 00:40:17,590
here this morning to give folks a sense
of the intent of the problem sets.

861
00:40:17,590 --> 00:40:21,270
Which ultimately are meant
to be very domain inspired.

862
00:40:21,270 --> 00:40:24,300
They're meant to be more
puzzle like than they

863
00:40:24,300 --> 00:40:29,040
are meant to be the more traditional
end of a chapter in a textbook problems.

864
00:40:29,040 --> 00:40:33,150
That just has you implement a very
small, very well defined problem

865
00:40:33,150 --> 00:40:35,310
like implement a function
that takes two arguments

866
00:40:35,310 --> 00:40:37,110
and return the sum of those two.

867
00:40:37,110 --> 00:40:41,440
Useful practice and good
reinforcement for muscle memory,

868
00:40:41,440 --> 00:40:45,660
but generally speaking for CS50's
own problem sets or weekly projects,

869
00:40:45,660 --> 00:40:49,680
the intent for us has long been to
take some inspiration from a real world

870
00:40:49,680 --> 00:40:50,650
problem.

871
00:40:50,650 --> 00:40:53,550
And even if at the end of the day,
the tools students need to solve

872
00:40:53,550 --> 00:40:57,540
it are pretty mundane like use
a loop, or use some variables,

873
00:40:57,540 --> 00:40:59,440
or some other feature of the language.

874
00:40:59,440 --> 00:41:03,550
We want them to approach the problem
with a much more alluring packaging

875
00:41:03,550 --> 00:41:04,050
to it.

876
00:41:04,050 --> 00:41:06,335
A much more alluring context.

877
00:41:06,335 --> 00:41:08,460
So that they actually see
the forest for the trees.

878
00:41:08,460 --> 00:41:12,000
And Brian, do you want to just
rattle off some of the domains

879
00:41:12,000 --> 00:41:14,438
that we've used successfully here?

880
00:41:14,438 --> 00:41:16,230
BRIAN YU: One of the
big goals has been to,

881
00:41:16,230 --> 00:41:19,080
since many students have never
really seen computer science before,

882
00:41:19,080 --> 00:41:21,420
to really emphasize how
much computer science can

883
00:41:21,420 --> 00:41:25,120
be connected to whatever it is that
students are already interested in.

884
00:41:25,120 --> 00:41:27,150
So if they're already
interested in games,

885
00:41:27,150 --> 00:41:29,490
there's a very early
problem set where students

886
00:41:29,490 --> 00:41:33,880
are building a pyramid as though it were
from the Super Mario Bros video game.

887
00:41:33,880 --> 00:41:35,880
And so, they see the connection there.

888
00:41:35,880 --> 00:41:38,430
For students that are maybe
interested in science,

889
00:41:38,430 --> 00:41:42,210
we've recently introduced more science
based problem sets where they're

890
00:41:42,210 --> 00:41:45,870
looking at DNA sequences, and
DNA sequences can really just

891
00:41:45,870 --> 00:41:48,010
be treated as a string of text.

892
00:41:48,010 --> 00:41:50,220
And so, all of the
opportunities for working

893
00:41:50,220 --> 00:41:53,230
with problems that are
manipulating strings of text,

894
00:41:53,230 --> 00:41:57,210
we can then apply to those sorts
of biology inspired problems.

895
00:41:57,210 --> 00:42:01,800
We can also apply them to problems
inspired by literature, taking examples

896
00:42:01,800 --> 00:42:04,440
from books from various
different grade levels,

897
00:42:04,440 --> 00:42:09,210
and assessing how difficult those books
might be to read all programmatically.

898
00:42:09,210 --> 00:42:12,413
And we've taken
inspiration from software

899
00:42:12,413 --> 00:42:15,330
that students are using, apps that
they're often using on their phone.

900
00:42:15,330 --> 00:42:18,690
Especially the filters that
apps like Instagram or Snapchat

901
00:42:18,690 --> 00:42:20,880
might be quite popular nowadays.

902
00:42:20,880 --> 00:42:24,270
And so we ask students when
we introduce files and images,

903
00:42:24,270 --> 00:42:26,610
to try building some of
those filters for themselves.

904
00:42:26,610 --> 00:42:29,490
Writing filters to apply
various different changes

905
00:42:29,490 --> 00:42:32,470
to existing images too.

906
00:42:32,470 --> 00:42:35,880
We explore the world of
cryptography and figuring out

907
00:42:35,880 --> 00:42:39,358
how to encrypt and decrypt information
in order to send secret messages.

908
00:42:39,358 --> 00:42:42,150
And ultimately, just trying to come
up with these sorts of problems

909
00:42:42,150 --> 00:42:44,550
that students will see
the practical value of it,

910
00:42:44,550 --> 00:42:46,030
and hopefully be excited by it.

911
00:42:46,030 --> 00:42:48,420
So that the problem
domain is interesting,

912
00:42:48,420 --> 00:42:51,150
and they're therefore able to
really get engaged with the code

913
00:42:51,150 --> 00:42:52,287
that they're writing to.

914
00:42:52,287 --> 00:42:54,620
DAVID MALAN: And for what
it's worth, the approach we've

915
00:42:54,620 --> 00:42:57,110
taken over the years to
finding problems like this,

916
00:42:57,110 --> 00:43:00,140
is just to keep a passive
eye and ear out over time.

917
00:43:00,140 --> 00:43:04,160
When we see some interesting blog
post online about some new technology,

918
00:43:04,160 --> 00:43:08,240
we start to think about how to distill
that seemingly complicated technology

919
00:43:08,240 --> 00:43:09,290
into its essence.

920
00:43:09,290 --> 00:43:12,560
For instance, like file recovery in
the forensics example that Brian gave.

921
00:43:12,560 --> 00:43:16,393
Or if we aren't ourselves
familiar with some field,

922
00:43:16,393 --> 00:43:18,560
for instance, the extent
of my background in biology

923
00:43:18,560 --> 00:43:20,870
is from ninth grade in
high school and that's it.

924
00:43:20,870 --> 00:43:23,870
Thankfully, Brian has a little
bit more of a background

925
00:43:23,870 --> 00:43:27,280
and was able to create our more
genetically inspired problems most

926
00:43:27,280 --> 00:43:27,780
recently.

927
00:43:27,780 --> 00:43:30,140
So that, even we are learning
something along the way.

928
00:43:30,140 --> 00:43:32,510
The upside of which is,
that we need to wrap

929
00:43:32,510 --> 00:43:34,550
our minds around a
complicated topic and then

930
00:43:34,550 --> 00:43:38,450
again distill it into something
simplified for students.

931
00:43:38,450 --> 00:43:41,420
But just so that they start to see
the connections of computer science

932
00:43:41,420 --> 00:43:43,525
and programming to these other worlds.

933
00:43:43,525 --> 00:43:45,650
As an aside, we see a whole
bunch of questions that

934
00:43:45,650 --> 00:43:46,790
have been flying across the screen.

935
00:43:46,790 --> 00:43:49,080
We're taking notes on all
of the chat questions.

936
00:43:49,080 --> 00:43:54,350
So even if we don't touch them all live
here, we'll follow up in some form,

937
00:43:54,350 --> 00:43:57,350
so as to not leave those unaddressed.

938
00:43:57,350 --> 00:44:00,080
So in closing here,
there's a few things we

939
00:44:00,080 --> 00:44:03,050
wanted to touch on as well as to
the events that we've done here.

940
00:44:03,050 --> 00:44:05,780
At least in healthier
times, CS50 has been

941
00:44:05,780 --> 00:44:09,170
punctuated at the beginning, the
middle, and the end of the semester

942
00:44:09,170 --> 00:44:13,190
by way of events that we've
brought online over time.

943
00:44:13,190 --> 00:44:15,940
We didn't start the course this
way, but each time over the years,

944
00:44:15,940 --> 00:44:18,357
did we try to introduce a
little something new to see what

945
00:44:18,357 --> 00:44:20,060
sticks and resonates with students.

946
00:44:20,060 --> 00:44:22,550
For instance, years ago, we
wanted to send the message

947
00:44:22,550 --> 00:44:26,390
very early on in the course,
before it begins practically,

948
00:44:26,390 --> 00:44:29,360
that computer science is not
about programming per se.

949
00:44:29,360 --> 00:44:32,450
And even though that's the mental
model that many students have,

950
00:44:32,450 --> 00:44:35,360
particularly given how it's
structured in lower grade levels,

951
00:44:35,360 --> 00:44:39,140
that it's programming-- we want
them to there see that it's not

952
00:44:39,140 --> 00:44:42,080
just what their friends have been
doing, middle school or high school,

953
00:44:42,080 --> 00:44:44,960
it's really about problem
solving more generally.

954
00:44:44,960 --> 00:44:47,630
And indeed, once you get to
college, at least in our case,

955
00:44:47,630 --> 00:44:49,520
are there are just so
many other directions

956
00:44:49,520 --> 00:44:50,952
that you can typically go in.

957
00:44:50,952 --> 00:44:53,660
And we want to give students a
taste of those various directions,

958
00:44:53,660 --> 00:44:57,980
but not by focusing on code
and on programming per se,

959
00:44:57,980 --> 00:45:00,380
but on taking input
and producing output.

960
00:45:00,380 --> 00:45:01,710
Ergo solving problems.

961
00:45:01,710 --> 00:45:05,000
So CS50 Puzzle Day is something
we've done for years with some alumni

962
00:45:05,000 --> 00:45:06,050
and friends at Facebook.

963
00:45:06,050 --> 00:45:09,830
We're really good at writing these
riddles and puzzles, mental puzzles not

964
00:45:09,830 --> 00:45:10,790
physical ones.

965
00:45:10,790 --> 00:45:14,330
And we print out a PDF of puzzles
at the start of the semester,

966
00:45:14,330 --> 00:45:17,637
we typically gather a few
hundred students in our case.

967
00:45:17,637 --> 00:45:19,970
And then, we make these same
puzzles available to anyone

968
00:45:19,970 --> 00:45:23,430
online, taking or
teaching CS50x or CS50 AP.

969
00:45:23,430 --> 00:45:27,320
So as to have a lot of these same
events localized in a local school,

970
00:45:27,320 --> 00:45:29,180
non-profit, or community, or the like.

971
00:45:29,180 --> 00:45:32,600
To really just get students excited at
the very beginning of the experience

972
00:45:32,600 --> 00:45:34,350
about solving problems.

973
00:45:34,350 --> 00:45:38,090
Toward the end of the semester, have
we typically done a CS50 hackathon.

974
00:45:38,090 --> 00:45:39,980
This too, is inspired
by a tradition that

975
00:45:39,980 --> 00:45:42,510
rather began in tech it would seem.

976
00:45:42,510 --> 00:45:47,960
But we gather in our case at
7:00 PM, and stay until 7:00 AM,

977
00:45:47,960 --> 00:45:50,630
working throughout the night,
which is not a time frame that

978
00:45:50,630 --> 00:45:52,260
works well for all grade levels.

979
00:45:52,260 --> 00:45:54,680
So we've also adapted
this idea over the years,

980
00:45:54,680 --> 00:45:57,380
we held a hackathon in
Manhattan a few years ago

981
00:45:57,380 --> 00:46:00,380
with a few public and a few
private schools for an AP audience.

982
00:46:00,380 --> 00:46:04,550
Focusing in that demographic
on, I think, 10 AM to 3 PM.

983
00:46:04,550 --> 00:46:07,970
And here I was thinking that 10 AM
was the ungodly hour on the weekend.

984
00:46:07,970 --> 00:46:11,430
But we adapted for the
different demographics as well.

985
00:46:11,430 --> 00:46:13,400
And so, this is an
opportunity in our case

986
00:46:13,400 --> 00:46:16,850
to either have students focus on
one of the course's problem sets,

987
00:46:16,850 --> 00:46:19,700
or some other programming project,
or their own final project

988
00:46:19,700 --> 00:46:23,000
depending on where in the school
year or the semester it falls.

989
00:46:23,000 --> 00:46:27,410
And it's just an opportunity
to normalize and socialize,

990
00:46:27,410 --> 00:46:28,940
what is effectively homework.

991
00:46:28,940 --> 00:46:32,150
But in a way that makes it feel like
a shared experience, and hopefully

992
00:46:32,150 --> 00:46:35,840
a memorable moment in their middle
school, high school or in our case,

993
00:46:35,840 --> 00:46:37,250
college career.

994
00:46:37,250 --> 00:46:39,140
And then lastly, is the CS50 fair.

995
00:46:39,140 --> 00:46:42,350
And Brian, do you want to speak to
exactly what happens at the CS50 fair?

996
00:46:42,350 --> 00:46:46,207
Whether on a small scale with one
class, or a large scale on campus?

997
00:46:46,207 --> 00:46:48,290
BRIAN YU: This is maybe
my favorite of the events.

998
00:46:48,290 --> 00:46:50,570
CS50 students typically
at the end of the class

999
00:46:50,570 --> 00:46:52,580
work on a final project
of their own choosing.

1000
00:46:52,580 --> 00:46:55,910
Where they get to decide on
something they're interested in,

1001
00:46:55,910 --> 00:46:59,000
and have the opportunity to
showcase it to others at the fair.

1002
00:46:59,000 --> 00:47:02,060
And so, we usually set up some
tables where students just

1003
00:47:02,060 --> 00:47:03,270
bring their computer.

1004
00:47:03,270 --> 00:47:06,740
And we invite other
teachers and students

1005
00:47:06,740 --> 00:47:09,860
from around the university to come
visit, and students from other schools

1006
00:47:09,860 --> 00:47:10,430
as well.

1007
00:47:10,430 --> 00:47:12,710
Just to come walk around
and talk to the students

1008
00:47:12,710 --> 00:47:14,653
and see what projects
that they've created.

1009
00:47:14,653 --> 00:47:16,820
And it's a really great
opportunity for the students

1010
00:47:16,820 --> 00:47:20,000
to have the chance to showcase what
they've been working so hard on.

1011
00:47:20,000 --> 00:47:22,130
And it's always inspiring
as a spectator, just

1012
00:47:22,130 --> 00:47:25,705
to go around and see all of the amazing
work that students have been doing.

1013
00:47:25,705 --> 00:47:28,080
DAVID MALAN: Well, I want to
be mindful of the time here.

1014
00:47:28,080 --> 00:47:31,400
So in a moment, let me turn things
back over to Carter and to Bernie

1015
00:47:31,400 --> 00:47:34,400
to give you a sense of what
more comes today and tomorrow.

1016
00:47:34,400 --> 00:47:38,000
Brian and I and the team will be
popping out and in of the sessions

1017
00:47:38,000 --> 00:47:38,990
today and tomorrow.

1018
00:47:38,990 --> 00:47:41,510
And by all means, always reach
out via email this weekend

1019
00:47:41,510 --> 00:47:42,950
or beyond if you have questions.

1020
00:47:42,950 --> 00:47:46,470
And for the chat questions we
didn't get to hear during the hour,

1021
00:47:46,470 --> 00:47:50,390
we will follow up on as many of
those as we can via email after this.

1022
00:47:50,390 --> 00:47:53,680
But thank you, and Carter, back to you.

1023
00:47:53,680 --> 00:47:55,000