Name: CS50 2017 - Lecture 1 - C
Uploaded: 2018-03-09T07:08:13.000Z
Duration: 1 h 26 min 37 s
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And you'll recall, of course, that just a few days ago, we

introduced programming and some fundamentals of computing

And today, we're going to build on those ideas

but begin to transition to a more cryptic looking

but nonetheless much more powerful language-- transitioning ultimately

So odds are by now, you had an opportunity with problem

set zero to experiment with Scratch and drag and drop puzzle pieces

and recall that the real point of Scratch,

beyond having a bit of fun in showing off,

which you can do with something like that,

is to explore ideas like loops and functions and conditions.

Maybe some Boolean expressions or events.

Really depends on how you pull those ingredients together.

But today, we introduce a language that's

decades-- called C. And it's an older language

and frankly, after CS50, odds are you're not likely

to use this language all that much, if ever.

But it's been a foundation for a lot of the more modern languages that

So roughly mid-semester when we transition to another language--

Python and then thereafter SQL and then thereafter

JavaScript-- you'll see a lot of those same origins and syntax and ideas.

And indeed, everything we did last week in Scratch, you're going to see

permeates all of these various languages.

Because at the end of the day, you're not learning C in CS50.

You're not learning Scratch or Python or JavaScript.

You're learning the fundamentals of computer science and ultimately,

So today, let's begin to translate some of last times ideas

into more cryptic looking but nonetheless fundamentally identical

So this was a super simple program that simply

displayed on the screen out of the mouth of a cat by default, hello world.

Well, let's begin to translate this to something textual

as most programming languages actually are,

we called an example of what kind of programming construct?

A verb or an action, do something in Scratch.

MIT decided to make them purple but that was just arbitrary

but they're consistent in the program because they're all

Now in C, starting today and for several weeks hereafter,

that same purple puzzle piece is going to start to look like this.

And we saw a glimpse of this last time-- printf, hello, world.

But notice there's a few salient characteristics

There's printf and we'll see what the f stands for today.

There's a parenthesis and a closed parenthesis over here.

And that kind of balance is going to be important, not intellectually, but just

syntactically because the computer is going

The quote and unquote, we'll see, surround words

So whereas last time in Scratch, you simply typed a word in a white box,

now you're going to do the same thing on your keyboard

And then lastly, there's going to be this nuisance, this semi-colon, which

a lot of languages have which simply says, end of thought.

It's like the programmer's equivalent of a period in an English sentence.

And you'll find that among the frustrations

that new programmers experience, myself included back in the day,

is you don't really notice these things from the get go.

And you might type out all of your logic and feel good

about your program try to run it and the thing doesn't work because of something

So the key takeaway for today especially is don't

You're absolutely going to bump against walls, not quite

seeing what someone like I might see after all these years of practice.

But in just a few weeks time, you'll start to notice patterns.

And the mistakes you might make in the first week

are going to be much more obvious to you in the second and third and beyond.

So this then would be a function in C. Let's

combine it as a complete program, which we did see a glimpse of last time.

So if you were to implement this same program,

hello, world in C, these are the several lines you would have to type.

Well, we can tease this apart by looking at just a few of the keywords

And some humans, years ago, just decided,

you know what, when another human is writing a program,

he or she has just got to call their function, as we'll soon see, main.

They could have called it anything they want

but main is kind of a nice word for it the main part of your program.

So this is the equivalent of our when green flag clicked in the language

Meanwhile, if we highlight another key word printf,

this is going to be the C equivalent of the say block in purple.

So printf is just going to print something on the screen.

Meanwhile, in yellow here now is what we're going to start calling a string.

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