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For Loops
4:55For loops, instantiate, check if they should terminate, and then run some code.
We've done do, while,
and we've done while,
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we got the pre-check, the post check.
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This one is the for loop.
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When you know how many times you want
to loop, this is a great example for
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when you want to use fors.
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They're often called the C style for loop.
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And it looks like a whole bunch of code
jammed into a little statement and
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it's a little overwhelming at first.
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Most C like languages implement them,
so you'll see it in Java Script,
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you'll see them all over the place.
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And it is an old school way
of looping over an array,
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which we'll talk about arrays here in a
little bit, if you haven't heard of them.
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But it's sort of an old school and
it's a little bit frowned upon, so
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let's just jump into it.
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Let's do 99 bottles of,
you know the old song,
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99 Bottles of Milk on the Wall,
right, right?
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Yeah, so, it's milk.
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So, you go 99 Bottles of Milk on the Wall,
99 Bottles of Milk, you take one down and
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pass it around,
98 Bottles of Milk on the Wall.
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So, that sort of thing.
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So, the for loop example, what we
would do here, is we'd start at 99.
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We're gonna start our loop at 99,
and as long as there's some,
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we're gonna take one off the wall,
and we're gonna sing about it.
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And we're gonna drink our milk,
and we're gonna throw it away, and
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then we're gonna go grab 98.
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So that's a for loop.
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This is the expression that's
happening and this is checking.
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And these three little
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new lines here have words and those words
also look a little bit intimidating.
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Let's talk about what they are.
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So, we have initialization.
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So that runs the very
first time this enters.
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So the very first time for
loop is encountered, initialization runs.
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That's where you want to set up different
variables that you're tracking stuff with.
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The second,
Java calls this thing a termination.
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What that is, if this statement
returns false it will terminate.
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This will run before the for loop goes and
then increment will happen afterwards.
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So, this statement runs and checks,
and if it returns a true or false.
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And if it returns true,
it continues looping.
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If it returns false, it stops.
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And the increment,
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what happens is, every time the loop
goes through, this statement will run.
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It doesn't have to increment
like we saw with the pluses.
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I'm using these words because this is
how it is in the Java documentation, but
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I find them a little bit confusing.
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What we're gonna do in this next statement
with our for loop, is we're gonna do
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99 Bottles of Milk on the Wall,
[LAUGH] I almost said the other thing.
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And it's going to count down.
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So let's do it.
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You can go refill your milks now,
if you'd like to.
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So milk, okay, so the for
loop looks like this.
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So this is where we're gonna initialize.
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Here we're gonna initialize
ta variable named i and
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i is going to be less than 99, okay?
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So as long as this is true,
we want to keep going, okay?
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So this is the termination.
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Then, each time we're gonna decrement,
okay?
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[LAUGH] In the increment
spot we're gonna decrement.
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So that's what minus, minus does, right?
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It says, i = i- 1.
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Decrementing by 1.
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Shorthand for doing that, okay?
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And then we'll say, %d,
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bottles of milk on the wall....
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And a %n, or that will get messy.
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With the %, not a /.
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Okay, and good, that's closed out.
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And we will compile Milk.
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>> [INAUDIBLE]
>> Oh, but you guys caught it, thanks!
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>> [APPLAUSE]
>> Thank you, that was awesome.
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Thanks, we're like peer programming
with 30, 40 people [LAUGH].
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>> [LAUGH]
>> [INAUDIBLE]
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>> [LAUGH] That's true [LAUGH].
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Okay, so-
>> So
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why are you having i
start at 0 [INAUDIBLE].
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>> You're right!
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Ken wow, [INAUDIBLE] double fail, wow!
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>> [APPLAUSE]
>> Thanks.
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Thank you.
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Would've been messy.
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All right here we go [LAUGH], I think it's
gonna work we've had a human compiler run-
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>> [LAUGH]
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>> [INAUDIBLE]
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>> Guys, what am I doing?
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>> [LAUGH]
>> You don't need me up here.
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All right, so,
[LAUGH] I was gonna start at 99.
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>> [LAUGH]
>> While i is greater than 0,
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we're going to decrement it and
keep going.
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Let's see if that works,
I bet it will [LAUGH].
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>> [LAUGH]
>> Can we edit that?
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Can we edit that that part?
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Hey, there it is!
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>> [APPLAUSE]
>> All right, wow.
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Okay, so we initialized and
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when this was false we terminated.
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And then each time we decremented through.
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