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Now that you know about while loops,

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let's talk about[br]another kind of loop, for loops.

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Here's a for loop I made to praise

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the most delicious kind of pizza,[br]pineapple pizza.

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You might think, "I liked while loops,"

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"Why should I care about[br]this new kind of loop?"

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Well, soon you will see[br]that a for loop is a way

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to write simple kinds of while loops[br]in a bit of a shorter way.

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So, before we inspect this for loop,

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let's go ahead and look at a while loop[br]which will be a bit more familiar.

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We'll get back to this for loop[br]in a moment.

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So, just like you saw[br]in the intro to while loops,

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We start with this variable <i>y</i>,

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and we write a message[br]using that location <i>y</i>.

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We say that we want to keep going

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as long as <i>y</i> is less than 300[br]and change <i>y</i> by 40 each time.

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Now, just to reinforce each of these,[br]which should be review,

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we can say that "Pineapple pizza is[br]the best" is an important message,

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so we probably want to be[br]writing it more.

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so we should start higher[br]--so we change that--,

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it should go on for longer,[br]so we make it bigger,

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and it should be spaced[br]closer together --don't you think?--

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so that's a little bit better.

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Now, let's see how we can change[br]this while loop into a for loop.

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I'm going to comment out this while loop,

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just so you can see that it's doing[br]what I'm saying it's going to do.

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And we'll create a for loop[br]and some space to fill in later.

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Something really important,[br]kind of different for a for loop,

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it's not just one thing that goes in here,[br]it's actually three things.

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We tell the computer that

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by using these semicolons[br]to separate the three parts,

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we'll have one part here,[br]one part here, one part here,

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and then, the inside of the loop,[br]just like we had before.

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So, what goes in each of these parts?

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You can think of it as a start,[br]or initialization,

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then we'll have a semicolon,

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then, some sort of instructions[br]on how long to repeat,

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and then we're going to have[br]some sort of change happening.

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So, how does that correspond[br]with this while loop?

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Really concretely, we can say

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that the start sets up[br]this variable <i>y</i> here,

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so let's copy and paste that over[br]to this first part of the for loop.

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Similarly, we can say[br]this middle part is saying

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how long we should keep going for[br]and that goes in the middle.

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We say the change happens at the end here,[br]we'll put that at the end of the for loop.

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These three parts always have to occur[br]in this order in your for loop.

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You always have to start by saying

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this is what the variable[br]should start out as.

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Here it's 27.

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Then you say how long to keep going for.[br]Repeat as long as it is less than 354.

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Then you need to put[br]how you are going to be changing things.

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So here we are going to be changing[br]by increasing <i>y</i> by 24.

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Last, you just have to do

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whatever you wanted to do[br]inside the for loop.

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So we'll go ahead[br]and write that text there.

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And there we have have it,[br]pineapple pizza is the best.

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Everybody will know.

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Now, let's think a bit more closely about[br]what's happening with this for loop.

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If we wanted to change where it started,[br]well, we just change the start here.

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If we wanted to change where it ended,[br]we just change this endpoint.

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If we wanted to change the spacing,[br]we would just change the increment number.

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We can also change[br]--just like with the while loop --

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what value we have for <i>x</i>.

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One thing that can be confusing[br]about a for loop

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is to remember what these semicolons do.

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You need to remember that they always need[br]to be there to separate the 3 parts.

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If we don't have them there,

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then we are going to get[br]some weird error messages

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about our for loop,

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so whenever you see[br]that just double-check that you have them.

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You also may get overenthusiastic[br]and add an extra one at the end,

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but if you just remember that semicolons[br]are only there to separate the 3 parts,

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then we can say that this last semicolon[br]isn't separating anything,

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it's just trailing on there, so we can[br]get rid of it because we don't need it.

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Now, I know you're probably[br]getting a little bit tired of seeing

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these for loops getting converted[br]into while loops and back,

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let's just do it one more time,

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so you can see a for loop really is

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just another way of writing[br]a simple kind of a while loop,

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and you'll be really confident[br]in understanding

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how to go from a for loop[br]back into a while loop.

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You can do that with any kind[br]of for loop, not just this one.

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The first thing that we do is think about

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where to put this first value[br]that we have inside of our for loop.

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Since it's just initializing[br]this variable,

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remember that it has to go outside[br]not inside the while loop,

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and it should go before as well,

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because we need to be using it[br]during our while loop.

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Then you think about[br]where should this condition go,

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--that's pretty easy--,

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usually the stop condition,[br]or the repeat until condition,

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needs to go inside here,

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we're gonna say while <i>y</i>[br]is less than 313 we'll keep going.

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Finally, the change.

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We always put the change[br]at the end of the while loop,

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in the loops that we've seen,[br]so we should go and do that here.

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Now, we just need to move this text call[br]inside, and there we have it.

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Comment out this whole loop, and you see[br]that we made the exact same thing happen.

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Hopefully by now, you can see

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that this new for loop[br]isn't actually necessary.

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We could go through our entire programming[br]lives writing loops that looked like this.

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But, it is a bit impressive[br]how much more concise this for loop is.

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It makes it a bit more clear,[br]once you're used to it, what's going on.

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How we're starting a variable,

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we're saying how long to keep going,

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and then changing that variable here.

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So, if you really hate for loops,[br]you don't have to use them ever,

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but you should be used to seeing them.

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And if they're confusing, just remember

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you can convert them back[br]into a while loop like this.

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And if you're feeling adventurous,[br]try using a for loop in your new program,

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or going back to some of your old,[br]simple while loops,

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and converting them[br]into for loops, if appropriate.

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A final note: you cannot always convert[br]a while loop into a for loop,

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only when they're[br]in a really simple form like this,

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where it's really clear[br]what variable you're starting out with,

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how long it's going for,[br]and how it's changing.