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code dot slash string.
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2.18
Ah, this is much prettier.
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1.48
Now I actually know what the computer wants me to do, give it a name.
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3.32
>> So I'm going to go ahead and type in Rob, enter, and hello, Rob.
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4.24
So, realize, this is still, at the end of the day, only a nine line program.
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3.62
But we've taken these baby steps.
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1.45
>> We wrote one line with which we were familiar, printf, hello world.
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Then we undid a little bit of that.
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1.6
And we actually used get string.
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And we tossed that value in a variable.
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1.802
And then we went ahead and improved it further with a third line.
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2.708
And this iterative process of writing software is truly key.
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3.15
In CS50, and in life in general, you should generally not sit down,
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4.2
have a program in mind, and try writing the whole damn thing all at once.
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3.38
>> It will, inevitably, result in way more errors than we ourselves saw here.
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4.01
Even I, to this day, constantly make other stupid mistakes,
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3.26
are actually harder mistakes that are harder to figure out.
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3.41
But you will make more mistakes the more lines of code you write all at once.
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4.615
And so this practice of, write a little bit of code
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that you're comfortable with, compile it, run it, test it more generally,
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3.71
then move on-- so just like we kept layering and layering last week,
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3.44
building from something very simple to something more complex,
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do the same here.
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1.01
Don't sit down, and try to write an entire problem.
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3.3
Actually take these baby steps.
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2.28
>> Now, strings aren't all that useful unto themselves.
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4.32
We'd actually, ideally, like to have something else in our toolkit.
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So let's actually do exactly that.
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2.78
>> Let me go ahead now and whip up a slightly different program.
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3.91
And we'll call this int.c, for integer.
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3.42
I'm going to, similarly, include CS550.h.
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I'm going to include standard IO.
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And that's going to be pretty common in these first few days of the class.
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>> And I'm going to ready myself with a main function.
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2.42
And now instead of getting a string, let's go ahead and get an int.
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4.32
Let's call it i, and call it get int, close parens, semi-colon.
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And now let's do something with it, printf.
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2.125
>> Let's say something like hello, backslash n, comma i.
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4.78
So I'm pretty much mimicking what I did just a moment ago.
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3.82
I have a placeholder here.
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1.65
I have comma i here, because I want to plug i into that placeholder.
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3.49
>> So let's go ahead and try compiling this program.
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2.1
The file is called int.c.
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2.81
So I'm going to say, make int, enter.
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2.86
Oh my God, but no big deal, right?
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3.5
There's a mistake.
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0.81
>> There's a syntactic mistake here such that the program can't
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2.58
be compiled inside int.c, line seven, character 27, error format
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5.65
specifies type char star, whatever that is.
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2.94
But the argument type is int.
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1.62
>> So here, too, we're not going to-- even though today is a lot of material,
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3.09
we're going to overwhelm you with absolutely every feature of C,
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2.6
and programming more generally, in just these first few weeks.
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So there's often going to be jargon with which you're not familiar.
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And, in fact, char star is something we're going to come back to
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in a week or two's time.
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>> But for now, let's see if we can parse words that are familiar.
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2.7
Formats-- so we heard format specifier, format code before.
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3.22
That's familiar.
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1.09
Type-- but the argument has type int.
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2
Wait a minute, i is an int.
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2.14
>> Maybe percent s actually has some defined meaning.
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3.25
And, indeed, it does.
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1
An integer, if you want printf to substitute it,
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2.871
you actually have to use a different format specifier.
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2.249
And you wouldn't know this unless someone told you,
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1.54
or you had done it before.
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1.083
But percent i is what can be commonly used
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in printf for plugging in an integer.
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1.75
You can also use percent d for a decimal integer.
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2.68
But i is nice and simple here.
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1.57
So we'll go with that.
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1.1
>> Now let me go ahead and rerun make int, Enter.
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That's good, no errors.
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2.168
Dot slash int-- OK, bad user experience, because I haven't told myself
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what to do.
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0.5
But that's fine.
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0.666
I'm catching on quickly.
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1.054
>> And now let me go ahead and type in David, OK, Zamila, Rob.
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6.78
OK, so this is a good thing.
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1.56
This time, I'm using a function, a puzzle piece, called get int.
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3.89
And it turns out-- and we'll see this later in the term--
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the CS50 staff has implemented get string in such a way
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that it will only physically get a string for you.
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>> It has implemented get int in such a way that it will only
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get an integer for you.
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And if you, the human, don't cooperate, it's
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literally just going to say retry, retry, retry,
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literally sitting there looping, until you oblige with some magical number,
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like 50, and hello 50.
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>> Or if we run this again and type in 42, hello 42.
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And so the get int function inside of that puzzle piece
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is enough logic, enough thought, to figure out, what is a word?
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And what is a number?
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Only accepting, ultimately, numbers.
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>> So it turns out that this isn't all that expressive.
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so far.
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So, yay, last time we went pretty quickly
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into implementing games, and animation, and artistic works in Scratch.
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And here, we are being content with hello world, and hello 50.
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