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We learned that loops can control how many times your code runs.

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And there are two types of loops, the loop, which runs code a specific number of times, and the wire

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loop, which runs code as long as something is true.

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Now, the for loop is good if you know in advance how many times something should run.

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And if you don't, then use a while loop.

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So in this lesson, you're going to understand when to use for loops and when to use while loops on

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top of learning how a while loop works.

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First things first.

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Inside your Section five folder, make a new class name the while loop Java.

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And here it has the main method.

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The while loop keeps running code, as long as something is true, the while loop is good.

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If you don't know in advance how many times a loop should run, because unlike the for loop a while,

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Loop doesn't have any fancy counters to keep track of how many times the code ran.

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It's just going to keep running the code as long as some condition remains true.

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So it stands to reason that the only thing a while loop needs is a condition and it's going to keep

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running until that condition turns false.

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Let's see how this works.

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In the world of class, I'm going to define a variable that stores a random integer and number is going

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to equal twenty five.

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Then I'm going to make a while loop, and this loop is going to keep running as long as that number,

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which we just defined is less than or equal to 30, as long as this condition remains true, this while

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loop is going to keep running and every time it runs, we're going to print that number.

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OK, I'm going to run the code.

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And to no surprise, the code runs forever.

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Now, don't panic, we can start the program by pressing control, see the supplies, the both Mac and

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Windows, and if you're using a Mac, it's control C, not command C, so that's really important.

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Now, the reason why this happens is because this condition that you see here, a number is smaller

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than or equal to 30.

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It's always going to be true because the number variable equals twenty five, which is smaller than

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30.

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And we're not doing anything to change that.

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So this condition is always going to be true and the loop is going to keep running forever.

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OK, so we need to fix our loop in that every time it runs, it needs to update the number variable

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by one and then eventually the variable is going to increase to 31, which will cause this condition

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to turn false and break the loop.

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So I'll run my code.

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And as I predicted, the while loop keeps running as long as the number is smaller than or equal to

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30, beyond which the condition turns false and the loop breaks.

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So from a diagram perspective, the loop runs six times.

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First, the number is twenty five.

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The condition is true.

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So the loop runs in.

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During each run we're increasing the number by one in our condition is going to remain true until the

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sixth run.

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Because in the sixth run, the number is going to increase to thirty one, the condition turning false

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and the loop breaks.

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Now, you know me, I like to visualize things from a runtime perspective, so this is how Java runs

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the wire loop first.

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The number is twenty five.

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So the condition is true.

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Prince twenty five and then inside the wire, updating the number to twenty six.

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Now the code inside the wire loop is done, but the condition is still true.

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It's going to keep printing and updating the number again and again.

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Now I'm just going to let this play out until we get to the sixth run.

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And here the number increases to thirty one, the condition turns false and the while loop breaks.

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Now, you might be asking yourself, shouldn't I have used the for loop instead?

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Yes, yes, you should have.

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The while loop that you created is very specific, and when you do run code a specific number of times,

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you need to use a for loop.

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In other words, when you know in advance how many times a piece of code needs to run, then use a for

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loop because the for loop combines the counter condition and increment in one line.

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If you ask me, it's a lot cleaner and the for loop is more compact.

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It's much easier to read and it was designed specifically for this purpose.

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So back in our code, we're going to reshape this into a for loop.

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We can put the start here.

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We can put the stop condition.

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And here we can put the step, the increment.

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And the fact that we can rewrite this while loop is a for loop so easily means that we shouldn't have

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been using a while loop to begin with.

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So I'm going to rerun the code.

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And we get the same output, but our code looks much nicer.

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Counter starts at 25 minute increments by one after each run, and it's going to keep running until

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I reach thirty one.

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At this point, the condition is false and the loop breaks.

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So when do I use a while loop, use a while loop, if it's not clear how many times the code should

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run, it's as simple as that.

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Let me give you an example.

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Delete the fallout, because this is a lesson on wire loops and I'm going to make two decimal variables.

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The first variable is some random number that you choose.

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Double choice is equal to zero point zero one.

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And I'm going to make another variable guess which for now is a random guess that I'm going to set to

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zero point nine nine.

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Now, I'm going to define a while, this while loop is going to keep running as long as gas is bigger

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than choice.

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In which case, I'm going to print hi, I'm in the wire loop.

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Rerunning my code.

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And to no surprise, the code runs forever because guess is bigger than choice, so the condition is

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always going to be true and the code is always going to run because we're not modifying guests in any

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way.

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So what I'm going to do is press control, see the stop the output once again, this applies to both

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Mac and Windows.

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Mac users do not press command, see press control, see.

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Now, back in my code, what I can do is inside the wire loop set guests equal to Mathoura random.

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And instead of printing the string, I'm going to print the gas variable so that you can see exactly

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what's going on.

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And so basically what I'm doing is the computer is going to keep guessing random numbers until it comes

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up with a number that's smaller than the choice which will turn the looping condition false.

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And when is that going to happen?

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We don't really know.

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The while loop is going to have to keep running while this condition is true and the loop is only going

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to break in the event that it comes up with a guess that's smaller than the number that you chose and

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that's going to be random.

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So we don't know when this loop is going to break, but let's just run our code.

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And check it out, our code keeps guessing and no and after many, many loops, after many, many iterations,

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it finally guesses a number that smaller than zero point zero one.

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In this case, zero point zero zero seven and the loop breaks.

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I'd like for you to be able to visualize this, so once again, here we have our condition, which starts

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off true because the guess is bigger than choice.

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So it keeps running.

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And after many, many loops, eventually it's going to guess a number that's smaller than choice.

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As soon as it does that, the condition is going to turn false and the loop is going to break.

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Now, the one thing I want you to take away from this is that it's impossible to know in advance how

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many times this code needs to run before Java comes up with a good guess.

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So this is a perfect use case for while loops, because unlike the for loop, a wire loop doesn't use

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counters to keep track of how many times each chunk of code needs to run.

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It's just going to keep running the code as long as some condition remains true.

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So remember, these rules use a for loop.

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If you know in advance how many times you need to run a piece of code and use a while loop to run code

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as long as something is true.

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In this video, you learn how to use a while loop and the while loop will keep running as long as some

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condition is true.

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First, you call it a wire loop that runs code exactly six times.

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But when you need to run code a specific number of times, a for loop is much better.

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It combines the start, the stop and the step in one line.

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It's more compact and it's much easier to read.

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But when you don't know how many times a piece of code needs to run, using a for loop is impossible

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because inside of a for loop, you need to specify exactly how many times it needs to run.

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So you needed to find a while loop that keeps trying to guess a number that's smaller than yours.

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It's impossible to know in advance how many times this code needs to run.

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So this was a perfect use case for why loops?

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So remember, these rules use a for loop, if you know in advance how many times you need to run a piece

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of code and use a while loop to run code, as long as something is true, that is really it.

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As long as you keep those two rules in mind, you should be good to go.

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And I think now you're ready to tackle the next three workbooks.

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Good luck.