While Loops

Quick reference

• 00:05 So in the last video, we looked at For loops, and
• 00:07 in this video I want to look at While loops.
• 00:09 For loops are a little complicated, there's lots of statements and
• 00:12 moving parts and all that stuff.
• 00:14 While loops are a lot easier.
• 00:15 So what does the While loop do?
• 00:17 Basically a While loop loops through a block of code as long as a condition
• 00:22 is true.
• 00:22 So they generally look like this.
• 00:24 Tab this over, so while a condition, while the condition is true, just do something.
• 00:31 So we can see already this looks a lot less complicated than the for loops,
• 00:35 a lot simpler.
• 00:36 And you'll kinda notice they sort of look like an If statement, right?
• 00:39 If (condition) do something.
• 00:41 while (condition) do something, very, very similar, right?
• 00:45 If you're comfortable doing If statements you're gonna be comfortable using
• 00:47 a while statement.
• 00:48 Maybe that's one of the reasons why I like while statements so much, but who knows.
• 00:51 So let's go ahead and build one real quick, very easy.
• 00:54 Now, For loops, in the last video we didn't have to declare our variable,
• 00:58 because it was done inside the loop.
• 01:00 Now we actually do have to declare our variable, 'cause it's not part of the loop.
• 01:04 So I'm gonna call a variable i and I'm gonna set it equal to 0.
• 01:08 So that's just creating a variable like we've done a bunch of times already.
• 01:11 So now here's the actual While loop part, let's go while, and
• 01:15 here's our condition, let's say i < 10.
• 01:18 So as long as i < 10, do something.
• 01:22 So we want to document.write, and let's say,
• 01:27 we wanna output the variable to the screen.
• 01:31 And let's give it a line break so it's not all on one line, and it's good to go.
• 01:36 Now, we need to do something else too.
• 01:38 We need to increment this inside the loop.
• 01:40 So let's go I++, remember, for our For loop we did it in the actual condition.
• 01:45 Here we have to explicitly do it inside the loop and
• 01:48 I'll talk about that in just a minute here.
• 01:50 So if we save this, hit Reload, we go boom, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
• 01:54 we started at 0.
• 01:55 That's why it starts at zero, as long as i < 10, you keep doing this.
• 02:00 Once it hits 10, the condition is no longer true so the loop stops.
• 02:03 So here I wanna talk a little bit more about this increment thing right here.
• 02:07 If we leave this off, what's gonna happen?
• 02:10 So we start out, our i is 0, so we see 0 is less than 10, that's true.
• 02:16 So it's gonna through here and execute this line of code.
• 02:18 It's gonna print out 0 in a line break and then it starts over again, it loops again.
• 02:23 Well, what is i?
• 02:24 Our i is 0 and 0 is less than 10, so it's gonna execute this line of code and
• 02:29 then loop again, and what is I?
• 02:31 I is 0, 0 is less than 10, so it's gonna execute this line and on and on and on.
• 02:36 And what we've got here now is an infinite loop.
• 02:39 It's just gonna keep spitting out 0, 0, 0, 0, 0,
• 02:42 0 because we forgot to increment it, right?
• 02:45 And believe me, you are going to forget to do this sometime in your computer
• 02:49 programming life.
• 02:50 I've done it probably a dozen times.
• 02:51 You create these infinite loops and your whole program just blows up and
• 02:55 it freezes up and everything stops.
• 02:57 I'm not gonna do it here, if you want to, you can leave out this line, save it,
• 03:00 come back here and hit Reload and see what happens.
• 03:03 Its just going to spit out a little line of zeros all the way down and
• 03:06 it's just going to keep scrolling and scrolling and
• 03:09 scrolling to infinity until your C9 thing crashes.
• 03:12 You're gonna actually have to close your browser and come back and
• 03:14 restart the whole thing in order to get out of it.
• 03:16 So very important like I said you're gonna forget,
• 03:20 you just do and you program is gonna crash because of it.
• 03:24 So when that happens to you, think back to this video and think hey,
• 03:27 John Elder told me this was gonna happen sometime, sure enough and sure did.
• 03:31 So that's the While loop, really quickly here there's another
• 03:35 way to do a While loop and it's just like this.
• 03:39 It's called the Do-While Loop, well, you can see this.
• 03:41 We're running out of time here.
• 03:43 So I'm just gonna create one real quick.
• 03:44 So basically a Do-While loop is, we still have a While loop down at the bottom, but
• 03:49 we have this block of code called the do and it gets executed at the top here.
• 03:54 This works out the same way as our old While loop,
• 03:56 it's just we explicitly put this stuff up here.
• 03:58 And one weird thing about this is this is gonna work no matter what, so if we change
• 04:03 our variable to 11, save this, it's still gonna spit it out one time, why?
• 04:09 Because this do part right up here gets executed before we hit the while.
• 04:13 So it will print this out one time, increase it, and
• 04:17 then now it'll say is 12 less than 10, no, and the loop will stop.
• 04:21 So it's just another variation of the While loop, the Do-While loop.
• 04:25 Honestly, I've never used the Do-While loop.
• 04:27 But it's something worth knowing and it's slightly interesting.
• 04:30 So those are loops, that's the While loop.
• 04:33 I tend to use the While loop more than other types of loops.
• 04:35 But it's all based on personal preference, use whatever you feel comfortable with.
• 04:39 In the next video we're gonna start to look at JSON.

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