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OK.

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Welcome to another lecture.

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We are now finishing up with our lectures on wildlife, and we are starting a lecture series on a new

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type of loop, which is called a for loop.

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So you might be thinking, well, why do we need another loop in a while, loop enough a loop as a loop,

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right?

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Well, technically, yes, you could use it while loops for everything, but there are certain situations

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which for Loop is actually easier to use and kind of more sensible.

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So take the below code simply.

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For example, this is from our last program that we had in the last lecture, actually.

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So you noticed that what we had to do was define a position variable set equal to zero an hour, while

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Loop was kind of based on that right?

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We said loop as long as position is less than five.

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But to make sure that everything worked out, we had to do a plus plus position.

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You can also do position plus plus.

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The problem is, if we forgot to do this, somehow we forgot to put this last line in here, which is

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easy, right?

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Because you define your condition, you're like, I want it to loop as long as position is less than

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five.

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Here I do the stuff I care about.

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And then you just put a close bracket and you forget this.

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It's really easy to forget this line right here.

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If we have to forget that the thing is that the loop would actually run infinitely.

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So I will show you that infinite loop today and the editor.

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You might have already seen that, though.

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So I could just be showing you again in that case.

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But the problem that that really arises is the reason why this is looking infinitely if we don't put

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this is because think about it, position is equal to zero, right?

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Well, if you look at this condition here, we're basically asking this year less than five, yeah,

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zero is less than five, so we run this stuff in here.

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Imagine this doesn't exist.

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Position is still zero.

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We go back to the top here and we ask is zero less than five we go down is zero less than five zero

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less than five zero less than five zero less, but it just keeps going over and over again.

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Zero is always less than five and position is always zero.

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So always going to be true, always going to run the loop.

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This condition is true and evaluates to true.

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It's going to keep going and going and going and going.

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Same thing for count.

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If we did not increment count, it would just be like count less than five.

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Well, yeah, count is zero zero less than five zero less than five zero less than five, and we just

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keep doing that.

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So if you had a lot of these loops in your program, it would be easy to make a mistake and get trapped

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in an infinite loop.

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And then you'd have to track that down.

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And if your code has like thousands of lines and it's happening in multiple spots like you fixed one

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infinite loop, then you had another one.

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It can get kind of annoying.

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It's just kind of a weird idea to have to put this in here if it was the only way.

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Sure.

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You know, you get used to it.

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It's fine, but the fact is, is that we know how many times we want to loop.

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The while it was kind of useful for when we want to just loop based on some condition, we're not really

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sure how many times.

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We need to loop, but we know for sure that we want to loop until something is like true or false.

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You know, and tell us some condition is met kind of would be intel.

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Whatever in here is evaluated to false because that's technically the syntax, right?

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But it's kind of more based on just a condition, right?

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Not not a certain amount of times, but this program we really cared about looping five times, right?

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Because we didn't we went win position was zero and one position was one in position with two in position

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with three in position was four.

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So that was five times and then one position was five.

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We did not run the code in here.

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So we knew from the get go that we hardcoded this array to five and that we were going to want to loop

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five times to get five numbers for each position of the array.

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This is where a fault gets becomes a lot better solution.

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So let's take a look at this.

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A for loop is useful for running for a specific number of iterations, which is what our program was

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doing right there.

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So for loop is better.

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So what we can do is that we can define the counter variable actually on the same line as the loop declaration,

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which is pretty cool.

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So you notice down in here, I have a for loop and right here rather than into position equals zero

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like we had above the well loop.

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We can put it in the same line actually inside the parentheses here.

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And this doesn't have to be I.

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It can also be position as we'll talk about here on the next slides.

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We're going to break this piece of code down with these three components.

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This one right here, this one right here and this one right here.

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So first off, you want to use the word four instead of while you have the same parentheses as the while

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loop, but it's going to have more stuff in it and then you'll also use the curly braces.

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So this part right here, this is what I was talking about with the interposition equals zero.

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So you don't have to use the character.

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I this is really just to define our counter variable, just like the interposition equals zero and you

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could have this equal and you can have this i b the word position instead.

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So position here, position here, position here.

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I sense for iteration, if you don't really know what to call the loop is kind of a de facto thing to

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call it.

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I that's just what a lot of programmers do.

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But you know, you should call it whatever makes sense for the program.

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So also note that you do not have to put this here, you can also put in A. equals zero above the for

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loop and then just leave this section blank this underline section, except for the semicolon, and

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then you would still have the rest of this in here.

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So let's look at the rest of this.

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What is the rest of this line?

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So after finishing this first part where we declare the counter, so we start off at zero, start our

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counter at zero.

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We now need to say how long we're going to have the Lupron, how many iterations, what is this condition

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based on the iterations?

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Well, we need to use a comparison operator for this.

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So what we're seeing right here is that I started zero.

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The loop is going to run while I is less than size, so that's how many times it will run.

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It will run from zero to size minus one, right?

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Once in his size, it'll actually break out of the loop and continue on with the program, the rest

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of the program.

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So starting at zero, going up to but not including size.

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So finally, we have to define what the increments will be.

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So here we're just doing a simple A-plus plus, so that means we're incrementing I buy one each time.

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You do not have to do A-plus, plus you do not have to just increment by one each time you can increment

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by whatever you like.

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You can use different operators in here and stuff.

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So the last few things, like I said, are the curly braces inside of the curly braces is where the

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magic happens.

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That is where all of the stuff that you want to run multiple iterations should go right.

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All the stuff that you want to be repeated multiple times for this amount of times.

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Is going to happen where it says do stuff here.

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And of course, that could be as many lines as you want.

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Similar to the wallet.

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So let's go ahead and head to the editor and modify that while the program to now instead use for loops.

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So here I just kind of already written it out.

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So what I'm going to do is kind of show you how this was.

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So this was just a while and then we had position less than five, right?

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That led us to have to have position equals zero here.

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We also had to have an eight count equals zero.

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And we have this + + position in the loop, but we don't need that anymore.

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We definitely don't need this + + position because what we can do in here is just put this part right.

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I copied pasted this here and then put how long the loop runs.

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And then I put my position +, +, +, +, + + position here.

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So here's the starting condition.

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Right.

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This is the start of this starting value for the iteration, for the variable cell position equals zero

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goes from zero up until five and it stops at five.

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So not including it's not going to actually run when position is five because it's positioned less than

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five.

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And then we have our increment right here on one line.

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For the count, we had the same thing, except what we did now.

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We don't need the count anymore.

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There was a count plus plus in here or actually it was plus plus count.

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We don't need that anymore because we have our.

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Incrementing happening right here before all that was in here, it was actually just this count less

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than five when it was a while loop instead of before.

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Now we have count less than five as this middle piece.

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We're starting at zero.

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Just like this in position equals zero.

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And that is our entire for loop.

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You notice that our program is a lot shorter now, a lot more concise.

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So this is something that you should be using when you know how many times you want to iterate over

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something.

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So specifically, we know the size of the array.

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That's why we should, instead of while loop use a for loop, right?

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So let's go ahead and just compile this so we can see what's going on.

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I'm just going to leave it as well.

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Loops to CBP.

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It probably should be changed to four loops if I was actually going to hold on to this, but I go ahead

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and compile it.

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So let's go ahead and run this wild to see.

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So you notice of yeah, I actually forgot to re say this then that a few times apologies for that.

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So recompile re run it services.

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Enter a number four position zero three three two two one five six.

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And then you notice that they all print out nicely in there.

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So, oops, I screwed up too much.

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So let's scroll up just a bit so I can get them on here.

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There you go.

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So here we have the same exact results that we had before for the while loop, except we did it in a

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much more clear and concise manner.

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So here I entered three two one five six and it printed out three two one five six.

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This part right here that I mistakenly had was from previous save right and we save, but that is something

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that I wanted to show you, which is what happens with the infinite loop.

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So let me go ahead and make another while loop here.

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Just in case you haven't seen the infinite loop, I want to show you this.

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So let's go back to this whole and position equals zero.

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So what I can do is, I say, well positioned less than five, because that's what we had, right?

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And then I'm going to go in here and I'm just going to say, see out, I'm in the side a loop and then

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put it in line, so we initialize it to zero.

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We say position less than five, but let's say we forget to do this classless position, you know,

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or position plus plus whatever thing we're going to do.

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And we just save it and run it.

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So I save this.

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Compile it, and I'm actually going to bring this up a little bit more.

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We run it.

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It just keeps saying over and over and over and over again, I'm inside a loop, I'm inside a loop,

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I'm inside a loop and it kind of just flashing the same thing.

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So you can't really see.

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But like if I was to put, let's just say I did something like this, like I said, position minus minus.

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And then I said, see out.

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Position, you know, here I'm changing the value of position, but it's changing in the wrong direction,

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we're still going to have an issue.

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So let's see what happens when I do this.

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It's a little funky there.

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Let me be clear.

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So looking at just counting down into negatives, just going and going and going and going and going,

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so this shows you a little bit different output that really gives you a better idea of this infinite

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loop that's just continuing to count down.

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All right.

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So that is why that is why sometimes the while loops can become sort of burdensome and it's better to

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use a for loop if the situation makes sense.

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If you know how many times you want to iterate, if you're iterating over some container that is specific,

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known size, maybe not directly known by you, but you're able to call some sort of function that gives

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you the size, anything like that, a good situation to use for that.

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OK, so this was just meant to be a basic introduction to four lips.

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The main things that I wanted you to take away from this are how to create a for loop what these things

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are inside of here, just as a quick recap.

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This is where the counter for the for loop starts.

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This is the condition in which how long before Liverpool run for and this is the incremental version

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of this counter for the for loop.

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So with that, I will see you in the next lectures where we will practice for loops just as we practiced

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while loops.