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Hey there.

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Welcome back.

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Let's go ahead and continue to expand our knowledge of the Lua programming language.

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This lecture is going to cover loops today a loop.

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And programming is a block of code that is continually executed until a condition is met.

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Some loops may execute for infinity, and others may execute for a set number of times.

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In Lua there are three loops you'll want to note the for loop, the while loop, and the repeat loop.

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The for loop is when you want to execute a block of code for an exact number of times.

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However, we can also use a for loop using this function called Ipairs to loop through arrays or tables

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that have index value pairs, and then we can also use the pairs function to loop through dictionaries

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or tables that have key value pairs.

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You can see one represents I for index and one amidst the I to represent key value pairs.

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The next loop we're going to take a look at is the while loop.

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And the while loop will continually execute a block of code until a specific condition is met.

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Or we can have them execute for infinity.

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And lastly is the repeat loop.

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And the repeat loop also continually executes a block of code until a condition is met, or we can execute

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them for infinity.

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Now you might say, isn't that the exact same thing as a while loop?

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Well, they are pretty similar, but there is one small difference that we're going to take a look at

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in a moment.

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Let's first go ahead and take a look at the for loop.

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Now, as I said, the for loop is for when we want to execute a code, a set or finite number of times.

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To create a for loop, we first type the for keyword, and afterwards we get to create a variable.

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And this variable is going to help us keep track at what iteration we are in our for loop.

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Most of the time we call this variable I, which stands for index, and we start at at a value typically

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of one.

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Next we're going to put a comma.

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And after this we're going to put the value or the number of times we want this for loop to execute.

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So for example maybe we want the for loop to execute ten times.

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So I would put ten here.

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And then we can put another comma.

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And this represents the number that we should increment I by each time we loop.

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So if I put one here that means I want to increment I by one each time through this loop.

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And that means this loop will execute ten times.

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However, if I put a number like two here, that means every single time through this loop I is going

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to be incremented by two instead, which will cut down the number of times this loop is going to be

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executed.

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And we can also omit the last number completely and just have two numbers.

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And that means by default our I will be incremented by one.

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After we do this, we're going to put another keyword down.

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And this is called the do keyword.

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And what the do keyword does is it creates a new scope.

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So if I hit enter, as you can see an n keyword appeared here because now we have a new scope that belongs

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to this for loop.

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Inside of this for loop I'm going to do is use our print function.

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And I'm going to print out I or our index into the console.

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So we can go ahead and go to our test tab and hit run.

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And as you can see here inside of our console, I has been printed one two all the way down to ten.

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So this for loop executed exactly ten times.

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And you can also see how fast this for loop executed.

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Because each time we get to see the milliseconds here, it took it one millisecond to execute it ten

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times.

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So it's almost instantaneous right.

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For loops are extremely quick.

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Now if I decided to put that third value in there and instead increment I by two each time, and then

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we hit run and we go ahead and look at the output.

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As you can see we started with an index of one.

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We added two to our one and we got three.

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And we keep adding two each time.

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And that means our for loop only executed half as many times or five instead of ten.

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And this is because once I has exceeded the value of ten, it's no longer going to execute.

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It basically checks for that condition and then it breaks out of our for loop.

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The next for loop, we can go ahead and take a look at is the for I pairs loop.

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And again as I said this is for looping through arrays.

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So what I'm going to do is I'm going to create a variable.

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We can call it example array.

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And we're going to create a new table here.

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And inside of this table we can just insert a bunch of random numbers like 32.

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We can put in 95 -1,043.4 50 -12.

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Right.

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So here we have an array with a bunch of different values inside of it.

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And what we're going to do is put our for keyword down again.

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But this time we're going to need to create two variables instead of one.

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And this is because we need one variable to store the index.

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And we need another variable to store the value at that index.

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So typically most developers name the first variable I.

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And then we put a comma afterwards.

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And then the second variable we typically call it v to represent value.

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Afterwards we have to use another keyword in Lua and this is called n and after this we need to pass

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a function that's going to act as the iterator.

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And an iterating function is simply one that is going to loop through all of the values in our table

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and return them back to these variables.

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And that is going to be the I pairs function.

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So as you can see right here, it turns an iterator function and the table for use in a loop.

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So we're going to use the I pairs function.

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And we get to pass our table here.

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So we'll pass example array.

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And then afterward we need to put another do keyword to create a new scope.

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And now what we could go ahead and do is print out the index and the value through each iteration of

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this loop.

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So I'm going to put a string here and I'm just going to say index.

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And then we concatenate this with I.

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And then we'll concatenate it with another string.

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And this time we're going to say value put another colon.

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And then we can concatenate this with v.

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So now this should loop through every single index value pair inside of our array.

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So through the first iteration we should get I of one and an I of one.

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We should get the value of 32.

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At the index of two we'll get 95 and so on.

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So let's go ahead and hit run.

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As you can see, here we go.

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We get index one and our index one.

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And we have the value of 32.

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At index two we have the value of 95 and so on and so forth.

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And as you can see it executes through our array chronologically.

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It starts at one and continues going through our array in order.

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Right.

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Because arrays have an order to them.

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They're organized.

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However, we know that dictionaries on the other hand, are not organized.

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And that's where the for pairs loop comes into play.

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So we're going to go through the exact same process as we did up here.

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I'm going to create a new variable I'll just call it example dictionary.

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And inside of here, we're just going to make some random key value pairs.

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I can call this first key something like data one and set it equal to 50.

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I'll create another one.

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Data two set it equal to 100.

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Data three.

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We can set to like 150 and then data four we can set to 200.

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So here we have our dictionary with our keys and our values.

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And what we need to do next is put our four keyword down.

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And the only difference I'm going to do here is instead of naming the first variable I, I'm instead

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going to name it K to let myself know that, hey, we're going to be looping through a dictionary that

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has key value pairs.

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So we have k and v key and value.

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And then we put our in keyword again.

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And this time we're going to be using the pairs function.

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And we can go ahead and pass our dictionary here.

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Put our do keyword down again and hit enter to create a new scope.

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And now what I'm going to do here is use our print function again.

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And this time I want to print out the keys so we can concatenate this with K and then concatenate that

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with another string.

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I'll just say value.

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Put a colon here and then concatenate that with v.

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So now we should loop through all of the different key value pairs in this table.

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And it's going to be printed out into our console.

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However what you're going to see is it's not going to print them in order.

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We might print data to first or we might print data for first.

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It's not going to be an order.

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And that's because dictionaries do not have an order to them.

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They're not like arrays.

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So if we go ahead and hit run here.

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As you can see, order was not maintained when we were looping through that dictionary.

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Data one got printed first with a value of 50, but then all of a sudden data three got printed next

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with a value of 150.

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Then data two with a value of 100 and then data four with a value of 200.

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So as you can see with our array, order was maintained but with our dictionary order was not maintained.

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Okay.

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So let's go ahead and take a look at the next loop here, which is our while loop.

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And these loops execute repeatedly until a condition is met.

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However, it's very crucial to note that these loops can be dangerous as they have the ability to crash

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our game if we do not yield the loop when it continually executes forever.

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What do I mean by yielding the loop?

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Well, when the main thread of execution hops into the block of code or the scope for that loop and

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starts executing, it needs to be able to yield or escape out of the loop at some point in order to

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execute other scripts in your game and other crucial engine tasks to keep the game running smoothly.

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When you have an infinite loop and it does not yield, it holds the main thread of execution hostage,

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and that thread will not be able to execute any other processes in the game engine which will cause

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the game to freeze and crash.

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The four loops that we took a look at here earlier do not require a yield, and that's because they

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are finite, right?

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They only execute a finite number of times.

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Even if you have a for loop that executes a thousand times, those executions will happen almost instantaneously.

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So a yield is not needed.

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But if we have a while loop that executes forever, we must yield the main thread of execution to avoid

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a crash.

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So I'm going to demonstrate to you what happens when we do not yield a while loop.

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To create a while loop, we type out the while keyword and after this while keyword, we need to create

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a condition to check.

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So this could be any condition in your game.

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Maybe you want to check if the value of a specific property is equal to another value, or you want

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to check if a number is greater than or equal to another number, whatever.

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But in this case, I want to create an infinitely executing loop.

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So all I'm going to do is just pass the value of true here.

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And then we put do again to create a new scope.

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And now we have created an infinitely executing loop.

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So our interpreter or the main thread of execution is going to start at the top of our script.

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It's going to go down through each of these for loops and execute every single one of them.

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And then eventually it's going to hit this while loop here, and it's going to hop into this while loop.

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And if this while loop does not yield, that thread is going to be stuck in here forever, which is

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going to cause our game to crash.

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So I'm going to do in this while loop is just print out like high into the console.

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And when I hit run you're going to see studio freeze and probably crash.

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So let's go ahead and see what happens.

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We hit run.

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And as you can see already, our game is refusing to load and my mouse is lagging.

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And there we go.

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Studio has just crashed.

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Thankfully, studio has an inbuilt feature where if it detects that the main thread of execution is

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stuck in a forever loop, then it will create a script timeout error and it says exhausted allowed execution

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time.

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So it recognized that our thread got stuck in an infinite loop and eventually stopped the game entirely

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and allowed us to go back to our script.

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But as you can see, having an infinite loop that does not yield is bad news for our game.

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All right, completely bad news.

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So now that we know the dangers of using while loops, your next question is probably going to be how

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do we yield out of a while loop?

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Well, we can do so by using a function in another library called the Task library.

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The task library holds several functions to help us manage the yielding and execution of our code.

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There's one function in the task library called task Dot.

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Wait.

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So to access the task library, I simply type out task and then index it.

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And here we can see several different functions.

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But the one we're going to take a look at here is the wait function.

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And here's the description it says yields the current thread until the next heartbeat in which the given

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duration in seconds has passed without throttling.

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So what this is saying is we pass a number to this function, and this function is going to allow the

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thread of execution to exit out of whatever block of code it's in.

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And then after that duration is up, it's going to hop back into that block of code it originally left

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and continue executing.

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So we can autofill this here.

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And we can go ahead and pass a number to represent how many seconds we would like to yield for.

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So if I put like one here, what's going to happen is the main thread is going to print hi in the console.

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And then it's going to encounter this yield function here.

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It's going to hop out of this while loop and start executing other important game stuff.

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And then once one second has surpassed it hops back into the original point and continues the next cycle

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of the while loop.

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So it'll print hi again, and then it'll go and yield again and continue doing this on and on and on

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for infinity.

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Now, if you leave this blank here, what's going to happen is this while loop is going to execute extremely

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fast.

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And this is because the default time duration for tasks wait is 0.016 seconds, which happens to match

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60 frames per second.

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This is because Roblox runs at 60 frames per second, and the time duration between each of those frames

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is 0.016 seconds.

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But for this example, I'm going to put the value of one here.

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And then if we hit run, you're going to see inside of our console every single second we're getting

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a new high printed out.

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So one second goes by get another high another second high high high.

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And it's going to continually do this for infinity.

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That's the purpose of an infinite while loop.

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We have a block of code that we want to execute forever and ever.

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Now we can also have our while loop act like a for loop, and it's a little bit more complicated.

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But what I'm going to do is I'll create a variable outside of my while loop.

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I'm going to call it I, and I'm just going to set it equal to the value of one.

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And then what I'm going to do is for my condition here, I'm going to check if I is less than ten.

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So as long as I is less than ten, we're going to execute this block of code here for our while loop.

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So I'm going to put I here and then to check if it's less than the value of ten.

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We use the less than symbol.

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And then we can put ten here.

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And we're going to do is we are going to increment I by one.

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So we're going to set I equal to itself.

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And then we're going to use the plus sign and add the value of one to I.

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So if I is one that means one plus one is two.

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We update the value in here to become two, and it's going to continually loop and do that.

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And then once the value of I surpasses ten or it's no longer less than ten, then this while loop is

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going to end because the condition has become false.

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So what I'm going to do here is I'm going to get rid of this yield statement, but instead I'm going

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to print out I into the console.

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And then we can go ahead and run our game.

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As you can see, I got printed as two and then three and then four, five, six, seven, eight, nine

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until it hit ten.

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And then once I has reached the value of ten, ten is not less than ten.

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So the condition became false and we broke out of that while loop.

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So as you can see, this while loop is acting the exact same as a for loop.

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It's just a little bit more complicated to do it this way.

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So that's why you would want to instead use a for loop.

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Okay, so the last loop we're going to take a look at is the repeat loop.

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This loop again is very similar to the while loop.

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But there is a slight difference.

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Before our while loop executes.

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Right.

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It first checks this condition up here.

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If this condition is already false, then this block of code is never going to have the chance to execute.

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However, with the repeat loop, instead of the condition being checked first, the condition is actually

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checked last.

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So that means if the condition is false at the start, it's still guaranteed to execute this loop at

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least once.

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So you'll see what I mean.

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To create a repeat loop, we type out the repeat keyword and then we hit enter.

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And then this next keyword gets automatically filled in here.

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And this is the until keyword.

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And after this until keyword is where we want to pass a condition.

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So as an example what I'm going to do is I'm going to set my I variable equal to we'll do zero.

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And inside of here we can print out I into the console and then we're going to increment I by one.

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So we do I is equal to I plus one.

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And then we don't want to continue looping once I becomes greater than ten.

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So this is reading out like basic English.

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Repeat this block of code until I becomes greater than the value of ten.

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So if we go ahead and hit run here.

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As you can see, we get ten iterations of our repeat loop.

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We print zero, one, two, three all the way to ten.

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And then once I has attained the value of 11, that is greater than ten.

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So our repeat loop has ended.

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Now I want to show you what happens if I is already 11.

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Right?

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If I is already 11, that means this condition has already evaluated to true and it will break out of

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this repeat loop.

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But that's not what's going to happen here.

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It's because we check this condition at the end.

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Meaning this block of code right here is guaranteed to execute at least once.

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So that means if we hit run here.

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As you can see, we still got it printed out inside of the console value of 11, right?

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We printed out 11 here, and then we incremented 11 by one, and then it finally broke out of the repeat

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loop.

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So actually what I'm going to do is I'm going to move this here.

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To be before our print statement.

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And then I'm going to run the game again.

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And as you can see, the value of 12 got printed out into the console, even though 12 is already greater

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than ten, right?

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It's because the condition is checked last.

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A repeat loop is always guaranteed to execute at least once.

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All righty.

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And that concludes this lecture on loops in Lua.

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I hope you've learned quite a lot and are ready to start putting these loops to use, because you will

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be using them a lot in your scripts.

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So get comfortable and I will see you in the next lecture.