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Narrator: So when should you use a while loop

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and when should you use a for loop?

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And it really depends on the problem you're trying to solve.

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For example, in a for loop

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I could do for item in,

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let's say a list, 1, 2, 3.

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And just looking at this code, you know right away

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that it's going to be looped over three times, right?

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And I could say here, print item.

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But you can do this in a while loop as well.

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I can say i equals to 0.

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And then while i is less

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than, let's say the length of the list,

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that is 1, 2, 3.

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Well, in that case I want you to print i

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or the item and then increment i by 1.

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If I run this, I see that, well technically here

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we're incrementing the i, which is the value,

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but let's say we had a list up here.

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So my_list, and this list will be 1, 2, 3.

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Well, my_list can be iterated with a for loop

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or it can be iterated with a while loop.

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And we simply say, my_list,

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at index of i.

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And if I run this, I get the same results.

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But, which one do you think is better?

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First off, while loops are very flexible.

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We can do a lot because we have this conditional statement,

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we can loop more than three times if we really wanted to.

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So in that case, while loops are more powerful

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but for loops are simpler, right?

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Like this code reads really nicely and really well,

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it makes sense.

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We just wanna loop over something that we already

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know how many times we wanna loop

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over, three times.

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With a while loop. We have to create this variable

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and we have to make sure we remember

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to increment the variable

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so we don't get an infinite loop.

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So with a while loop, you need to make sure we remember to

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halt the loop at some point.

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So my rule is usually this.

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For simple loops or iterating over iterable objects

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for loops are great.

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But let's say you are not sure how many times you wanna loop

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over something, you're not really sure how long

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it's going to take for looping.

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So you wanna say while something is true, just keep looping.

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For example, let's say we're trying to go through an email

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list that we've collected on a website.

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And for each email list we wanna send an email,

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Well, while the list is still there,

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let's just keep sending emails.

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There are many, many cases,

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but one of the most useful ways

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to use the while loop is like this is.

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Is to say, while true, do something.

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And make sure that at the end we break.

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Hold on what's happening here?

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I'm saying while true

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wouldn't that create an infinite loop?

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I mean, true is always going to be true.

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And you'd be right if you notice that.

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But again, we have a break statement here,

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so at the end, after we run line three, it's going to break.

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But now we can do something powerful like input here.

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And if you remember an input is going to ask us for a prompt

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to enter something.

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So I can say, hey, input, say something.

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And if I click run, it's going to say, hey, say something.

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You know what? Let's add semicolon here

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or a colon here and let's try that again.

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And look at that. It's saying say something.

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I'm on line three right now, so I'm going to say hi.

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And did you see that? We just broke out of the loop?

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It only asked me once, even though this was true

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as soon as we got to line four, I was done.

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But what if I removed this and I click run.

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If I say something, I say hi.

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And then it asks me again, Hi, Hi. I'm telling hi.

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And it keeps asking me, asking me, asking me,

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and we have an infinite loop.

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But the interesting thing here is

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that we can use conditional logic, right?

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What if we said response here

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and collect whatever the response is and say

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if response is equal to, let's say bye

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then I'm going to break.

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So that if I run this again,

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I say hi keeps asking me, and you know what?

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I'm getting annoyed with you machine. I'm going to say bye.

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It's going to exit it out for me.

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How cool is that?

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So while loops are extremely useful for tasks

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like this where looping can happen for a long time

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you don't know how many times it's going to happen.

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But this is something that you're just going to

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have to get used to with practice.

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Eventually, and I promise you

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this happens where you'll figure out

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when to use while, when to use for loop.

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But at the end of the day, use whatever solves your problem.

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I'll see you in the next one. Bye-bye.