Oh Mama David Milan hablo un poco espanol.

But this will be in English, if that's OK as this morning, but so nice to see some familiar faces and some new ones as well.

As Jose said, We thought we'd give you an introduction to computer science, the goal of which is to empower youto have more technical conversations, perhaps with those students were taking Jose's class right now or those of you who are first years.

You might like to take Jose's class next semester or beyond.

Please feel free to join us in CS 50 and in Kai Esso.

Computer science is something that's unfamiliar to a lot of people.

For instance, what is computer science?

Anyone who's not in Jose's class, What is computer science?

Gonna have to call?

See?

No one's put up.

Very few people put up their name tags in this one.

That's okay.

Cares Latin from Attica.

Anyone at all?

Anyone at all?

It's all right.

Someone.

How about this from Jose's class?

What is computer science?

Yes, please.

It's the way that computers work.

OK, computer language.

Okay, hero.

No, a way to be broken.

Okay.

Like translate from Arlen.

Good I really like that.

So it's the study.

It's getting computers to do what we want them to do.

And more generally it's the study of information and like the processes around information that allow you to actually solve problems.

And frankly, this did not.

This was not clear to me when I first was able to study computer science way back in high school.

Even in last quail a secondary.

I did not study computer science because I thought it was only about programming, and it seemed very anti social, and everyone's heads were down in the computer lab, and they seemed very focused only on the keyboard.

But really, it wasn't until college when I took a course called CS 50 that I discovered that it really is more generally about problem solving.

And what's exciting about computer science is that it's not just useful within the domain of computer science and Purcell analyzing data and information.

But it really is something that you can bring back to your own world, whether that's in the physical sciences, natural sciences, arts, humanities, business or the like, because it's really all about teaching you computational thinking.

It cleans up your thinking process.

It helps you think Maur logically.

It helps you express yourself more precisely more correctly.

And as such, it just makes you a much better communicator and, ultimately decision maker.

And so with that said, Let's start really at the beginning, What does it mean to think?

Computational e What means to think methodically more carefully or as well, Seymour Algorithmic Lee, so to speak.

And what does it mean to solve a problem?

Well, I'd propose that it really is just this.

Any problem in the world just has some input, the problem that you want to solve and you want some solutions.

So we'll call that the output.

And in between, here is some kind of process, some kind of problem solving mechanism that actually gets the job done.

But it's pretty fair to say that this is computer science, at least at a very high level.

But before we can discuss inputs and outputs, we like a computer.

Scientists need to decide how to represent information.

After all, at the end of the day, our computers, our phones only have say electricity, so we really all need to agree in advance how we somehow use electricity to represent inputs and outputs.

And it's kind of funny that I just counted the two ingredients to this problem.

How might we represent information If we're just counting information, the number of people in the room will 12345 Or I could count higher certainly if I used hash marks one, 23456 and so forth.

And so that actually that process has a name.

It's called Who?

Neri notation, You know, implying one.

And that's just because you have one single mark or one type of digit of finger via which you can count people.

So just a casual, warm up exercise.

Because there's a lot of folks who obviously don't know much about computer science.

We would call you back home those less comfortable and that's totally fine.

That's the largest demographic of students taking CS 50 back home.

How high can I count?

On one hand, I hear five six.

Okay, um, six is not right, but it is not five.

It's not five.

You're all wrong somehow.

Well, why is that?

Well, odds are if you like me, you start counting pretty reasonably like 12345 Okay, now we're out of fingers.

Unless we start using the secondhand, so five would seem to be the highest.

But that's because I didn't really think very hard about this problem and represent the information as efficiently as optimally as I might be able to write.

I'm just putting my fingers up or down, but I'm really taking no into it, not intake.

I'm not even taking into account the order in which I'm raising or lowering my fingers.

What if instead, this still represent zero?

I've not counted anyone yet.

But what if I do?

This is one.

And then maybe this is too.

And then this is three.

And then if we keep counting it slightly offensive in some cultures, this is four.

This is then five.

This is then six.

This is now seven.

So even if you didn't quite follow the exact pattern I was doing, it was obviously not as simple as 12345 I was instead kind of per muting them in different ways by raising and lowering them, thereby making a pattern out of them.

And so in that case, it actually is significant.

If my finger is up or it's down, that is, there's two states my finger could be in.

It's not just that there's a hash mark there or not my fingers either up or down proactively.

And that's called binary notation by implying, too.

And it's because each my fingers can either be down or up.

Or we might call this off or on, or zero or one, but more on that in just a moment.

So, in other words, I can actually count much higher than five with five fingers.

Does anyone know where want to do the math?

How high can I count?

Yeah, it's 31.

It's very painful to count the 31 on your five human fingers because I don't think I can arrange My fingers is quite cleanly enough to do that.

But there are indeed 32 total patterns off fingers up and down on just one hand.

If I started zero and I go up to all five, there's 32 total.

But if this is zero and this is all up, then if I've got 32 possibilities, I can count from 0 to 31 it turns out, but more on that in just a little bit, so that's a lot.

And that suggests that with a little bit more thoughts and a little bit more cleverness as to how a computer scientist represents information, you can pack a lot more information into very limited space.

So how do we get those from culinary toe binary to computers?

Well, at the end of the day, you probably all know or have heard that computer's only understand binary zeroes and ones.

So what does that really mean?

Well, it turns out that computers, even though they might seem pretty sophisticated, they're pretty dumb devices, right?

They only first of all, do what we tell them to dio.

And that's the power is Priscilla notes of getting a computer to do something for you.

But moreover, they only take one simple input.

They take like electricity from the wall, or maybe from your battery.

And even if you've not studied electricity, it's, you know, electrons flowing in or out of the device, somehow powering the device.

That's the Onley physical input.

And so how perfect is it that there's a way to represent information by either putting a finger down or up or off, or on that is two different states because you can represent two states really easily.

For instance, my laptop right now is on, and thankfully it has battery.

Now it would be potentially off because it's not plugged in on electricity flowing or off.

So why is this Germaine?

While a computer, it turns out, can represent information just by storing or not storing electricity?

And that's powerful because you can somehow use electricity either on our offer, on or off and represent.

It turns out different numbers, but what are those numbers going to be?

Well, consider this even if you've never Well, let me ask a question first.

How many of you can speak binary or understand binary, right?

Priscilla and few other people.

OK, so most people not.

But it turns out, give me like, two minutes and everyone in this room will be able to Why?

Well, first, let's start where we all started as kids.

If you saw this on the board, this is of course, what number?

Yeah, 123 right?

It's all very intuitive to us.

But why, really?

All I did was draw three symbols on the board.

I kind of went like this and then this kind of curvy stroke and then a slightly more curvy stroke and drew the symbols on the board.

But you all sort of instinctively assigned meaning to each of these symbols and quickly, mathematically got to 123.

But why is that?

Well, if you're like me in the U.

S.

I grew up learning that this is kind of the ones place with one's column.

This is the tens place or the tens column.

This is the hundreds place with hundreds column and then so forth to keep multiplying by 10.

And so the reason that 123 is 123 is because this is technically 100 times one, and this is 10 times too.

And this is one times three.

That, of course, is 100 plus 20 plus three.

And this, of course, is 123.

Now, this might seem like circular logic, cause I've literally written down the same thing.

But now we've described meaning to do look positions of each of those symbols on the board.

Now, what are these places really representing not to get too technical, but their just powers of 10 right?

The ones place is technically 10 to the zero, cause tens of the zero is one.

The next place is actually 10 to the one intend to.

The one is 10.

This is of course, 10 squared or tend to the two.

And that gives you 100 so tend to the three tens of the 4 10 to the five.

These are just powers of 10.

So a computer and most of you a moment ago claim not to speak binary.

Ah, computer is fundamentally really the same exact thing.

Except each of the places is not a power of 10.

It's probably a power of to instead, right?

We humans sort of now naturally these days speak decimal dec meaning 10 and that 0123456789 Computer turns out, speaks binary and by convention, ah, computer only understand zero in one.

And that might seem very limiting at first glance.

But if this is the ones place now, this is the twos place.

This is the fourth place than 8 16 32 We can represent the exact same numbers just with different patterns.

But now the symbols I can draw are not zero through nine.

They're zero through one, so a little more limiting.

But that's okay, because the columns will allow me to do the same kind of math.

So, for instance, given this logic, if the only two things I can write with this talk is a zero or a one, how do we represent in binary?

That is zeros and ones only.

The number we humans know as zero.

Yeah.

Yeah.

So 000 It's kind of trivial.

Why?

While just four times zero plus two times zero plus one time zero is still zero.

So that one's not that interesting.

How would we represent the number we humans know in decimal as one 001001 And this is where it might get a little tricky for a moment.

How about two?

Yeah, 010 And this is where Now we see the connection to what I was doing with my fingers.

I didn't go 012 The second time, I went 012 thereby changing my finger from like a 1 to 0 and zero to a one to give me this pattern and Of course, if you want to represent three, it's gonna be Yeah, 011 And now, how about seven?

Yeah, 111 Right, cause that's four times one plus two times one plus one times one.

So four plus two plus one is seven.

And then maybe your question, how do we represent eight?

Yeah, we need another place holder, and that's fine.

You know, if if we were on a piece of paper or a board, I can, of course, just write a one here.

And then these, of course, now need to become zeros because implicit to the left here was gonna be the eights place, even though I don't need to write it from the gecko.

But there's now a limitation.

Computers, of course, or physical devices.

And even if you have the fanciest of Macs or PCs like you only have so much room in that computer, you only have so much memory, so much hardware.

So it's certainly finite.

And so let's actually dive down into what's inside of a computer such that you can actually represent the number seven or eight or anything in between using an actual computer.

Well, turns out that inside of a computer are in simple form, just like lots of tiny little light bulbs or, more specifically, little switches that could be turned on and off.

And those switches, when turned on and off, either allow you to store a little bit of electricity that came from the wall or the battery or allow it to dissipate and go away.

So those switches air called transistors.