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because it doesn't look like you really need them.
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2.14
They don't really complete your thought like a parenthesis or a curly
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3.25
brace does.
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0.924
Let's go ahead and recompile the code and see.
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1.916
So make switch, dot slash switch.
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4.06
Let's type in lower case y, the top case, Enter.
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2.745
So I typed y.
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1.31
>> The program said yes, no, error, as though it was changing its mind.
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3.72
But it kind of was, because what happens with a switch is the first case that
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4.86
match essentially means, hey computer, execute all of the code beneath it.
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4.619
And if you don't say break, or don't say break, or don't say break,
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2.791
the computer is going to blow through all of those lines
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2.85
and execute all of them until it gets to that curly brace.
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3.239
So the brakes are, indeed, necessary.
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1.541
But a takeaway here is, when in doubt, try something.
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2.8
Maybe save your code first, or save it in an extra file
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2.39
if you're really worried about messing up and having to recover
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3.42
the work that you know is working.
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1.5
>> But try things.
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0.98
And don't be as afraid, perhaps, of what the computer might do,
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2.664
or that you might break something.
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1.416
You can always revert back to some earlier version.
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3.3
>> So let's end by looking at the design of code.
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2.85
We have this ability now to write conditions, and write loops,
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3.38
and variables, and call functions.
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1.83
So, frankly, we're kind of back at where we were a week ago with Scratch,
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3.74
albeit with a less compelling textual environment than Scratch allows.
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5.53
>> But notice how quickly we've acquired that vocabulary, even if it's
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3.87
going to take a little while to sink in, so that we can now use this vocabulary
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3.58
to write more interesting programs.
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2.75
And let's take a baby step toward that, as follows.
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2.62
Let me go ahead and create a new file here.
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1.95
>> I'm going to call this prototype.c, and introduce
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2.86
for the first time, the ability to make your own functions.
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3.204
Some of you might have done this with Scratch,
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1.916
whereby you can create your own custom blocks in Scratch,
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2.56
and then drag them into place wherever you'd like in C.
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2.462
And in most programming languages, you can do exactly
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2.208
that-- make your own functions, if they don't already exist.
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3.48
>> So, for instance, let me go ahead and include CS50.h, and include
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5.08
standard IO.h, int main void.
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4.45
And now we have a placeholder ready to go.
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2.91
I keep printing things like people's names today.
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2.53
And that feels like-- wouldn't be nice if there
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3.36
were a function called print name?
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2.026
I don't have to use printf.
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1.124
I don't have to remember all the format codes.
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1.916
Why don't I, or why didn't someone before me,
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3.074
create a function called print name, that given some name,
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2.93
simply prints it out?
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1
>> In other words, if I say, hey, computer, give me a string
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4.72
by asking the user for such, via CS50's get string function.
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3.17
Hey, computer, put that string in the variable in the left hand side,
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3.22
and call it s.
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1.06
And then, hey computer, go ahead and print that person's name, done.
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6
>> Now, it would be nice, because this program, aptly named,
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4.09
tells me what it's supposed to do by way of those function's names.
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2.93
Let me go and make prototype, Enter.
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3.76
And, unfortunately, this isn't going to fly.
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2
>> Prototype.c, line 7, character 5, error, implicit declaration
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4.5
of function print name is invalid in C99, C99
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3.53
meaning a version of C that came out in 1999.
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2.17
That's all.
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0.6
>> So I don't know what all of this means yet.
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3.05
But I do recognize error in red.
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2.03
That's pretty obvious.
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0.96
>> And it seems that with the green character here,
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1.999
the issue is with print name, open paren s, close paren, semi-colon.
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3.751
But implicit declaration of function we did see briefly earlier.
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4.28
This means, simply, that Clang does not know what I mean.
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3.08
>> I've used a vocabulary word that it's never seen or been taught before.
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4.12
And so I need to teach it what this function means.
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2.95
So I'm going to go ahead and do that.
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1.64
>> I'm going to go ahead and implement my own function called Print Name.
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4.38
And I'm going to say, as follows, that it does this, printf, hello, percent
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6.75
s, backslash n, name, semi-colon.
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3.04
So what did I just do?
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1.49
>> So it turns out, to implement your own function,
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2.075
we kind of borrow some of the same structure as main
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2.52
that we've just been taken for granted, and I
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1.875
know just copying and pasting pretty much what
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2.01
I've been writing in the past.
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1.44
But notice the pattern here.
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1.4
Int, Main, Void, we'll tease apart before long what that actually means.
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3.18
>> But for today, just notice the parallelism.
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2.41
Void, print name, string name, so there's
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2.05
a purple keyword, which we're going to start
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2.1
calling a return type, the name of the function, and then the input.
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3.757
So, actually, we can distill this kind of like last week
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2.333
as, this is the name or the algorithm of the code we're
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2.63
going to write-- the algorithm underlying
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1.731
the code we're going to write.
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1.249
>> This is its input.
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1.17
This is its output.
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1.49
This function, print name, is designed to take a string called name,
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4.06
or whatever, as input, and then void.
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2.62
It doesn't return anything, like get string or get int does.
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2.554
So it's going to hand me something back.
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1.666
It's just going to have a side effect, so to speak,
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2.39
of printing a person's name.
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1.61