For Loops4:55 with Craig Dennis
For loops, instantiate, check if they should terminate, and then run some code.
We've done do, while, and we've done while, 0:00 we got the pre-check, the post check. 0:02 This one is the for loop. 0:04 When you know how many times you want to loop, this is a great example for 0:07 when you want to use fors. 0:10 They're often called the C style for loop. 0:12 And it looks like a whole bunch of code jammed into a little statement and 0:14 it's a little overwhelming at first. 0:18 Most C like languages implement them, so you'll see it in Java Script, 0:20 you'll see them all over the place. 0:23 And it is an old school way of looping over an array, 0:25 which we'll talk about arrays here in a little bit, if you haven't heard of them. 0:28 But it's sort of an old school and it's a little bit frowned upon, so 0:31 let's just jump into it. 0:35 Let's do 99 bottles of, you know the old song, 0:37 99 Bottles of Milk on the Wall, right, right? 0:40 Yeah, so, it's milk. 0:44 So, you go 99 Bottles of Milk on the Wall, 99 Bottles of Milk, you take one down and 0:47 pass it around, 98 Bottles of Milk on the Wall. 0:51 So, that sort of thing. 0:53 So, the for loop example, what we would do here, is we'd start at 99. 0:54 We're gonna start our loop at 99, and as long as there's some, 0:59 we're gonna take one off the wall, and we're gonna sing about it. 1:02 And we're gonna drink our milk, and we're gonna throw it away, and 1:05 then we're gonna go grab 98. 1:07 So that's a for loop. 1:08 This is the expression that's happening and this is checking. 1:09 And these three little 1:14 new lines here have words and those words also look a little bit intimidating. 1:18 Let's talk about what they are. 1:23 So, we have initialization. 1:24 So that runs the very first time this enters. 1:26 So the very first time for loop is encountered, initialization runs. 1:29 That's where you want to set up different variables that you're tracking stuff with. 1:32 The second, Java calls this thing a termination. 1:36 What that is, if this statement returns false it will terminate. 1:39 This will run before the for loop goes and then increment will happen afterwards. 1:43 So, this statement runs and checks, and if it returns a true or false. 1:47 And if it returns true, it continues looping. 1:51 If it returns false, it stops. 1:53 And the increment, 1:54 what happens is, every time the loop goes through, this statement will run. 1:55 It doesn't have to increment like we saw with the pluses. 1:59 I'm using these words because this is how it is in the Java documentation, but 2:01 I find them a little bit confusing. 2:05 What we're gonna do in this next statement with our for loop, is we're gonna do 2:07 99 Bottles of Milk on the Wall, [LAUGH] I almost said the other thing. 2:10 And it's going to count down. 2:13 So let's do it. 2:16 You can go refill your milks now, if you'd like to. 2:16 So milk, okay, so the for loop looks like this. 2:21 So this is where we're gonna initialize. 2:28 Here we're gonna initialize ta variable named i and 2:30 i is going to be less than 99, okay? 2:33 So as long as this is true, we want to keep going, okay? 2:37 So this is the termination. 2:40 Then, each time we're gonna decrement, okay? 2:43 [LAUGH] In the increment spot we're gonna decrement. 2:46 So that's what minus, minus does, right? 2:49 It says, i = i- 1. 2:51 Decrementing by 1. 2:55 Shorthand for doing that, okay? 2:57 And then we'll say, %d, 2:59 bottles of milk on the wall.... 3:05 And a %n, or that will get messy. 3:13 With the %, not a /. 3:16 Okay, and good, that's closed out. 3:19 And we will compile Milk. 3:25 >> [INAUDIBLE] >> Oh, but you guys caught it, thanks! 3:30 >> [APPLAUSE] >> Thank you, that was awesome. 3:34 Thanks, we're like peer programming with 30, 40 people [LAUGH]. 3:37 >> [LAUGH] >> [INAUDIBLE] 3:41 >> [LAUGH] That's true [LAUGH]. 3:44 Okay, so- >> So 3:48 why are you having i start at 0 [INAUDIBLE]. 3:49 >> You're right! 3:53 Ken wow, [INAUDIBLE] double fail, wow! 3:55 >> [APPLAUSE] >> Thanks. 3:57 Thank you. 4:00 Would've been messy. 4:01 All right here we go [LAUGH], I think it's gonna work we've had a human compiler run- 4:03 >> [LAUGH] 4:08 >> [INAUDIBLE] 4:09 >> Guys, what am I doing? 4:14 >> [LAUGH] >> You don't need me up here. 4:15 All right, so, [LAUGH] I was gonna start at 99. 4:18 >> [LAUGH] >> While i is greater than 0, 4:21 we're going to decrement it and keep going. 4:25 Let's see if that works, I bet it will [LAUGH]. 4:28 >> [LAUGH] >> Can we edit that? 4:30 Can we edit that that part? 4:33 Hey, there it is! 4:34 >> [APPLAUSE] >> All right, wow. 4:36 Okay, so we initialized and 4:40 when this was false we terminated. 4:44 And then each time we decremented through. 4:49
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