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‫Hello and welcome.

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‫In this lecture, we're going to be investigating the concept of local variables, variables that only

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‫exist within a given function.

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‫And we're going to see how we can use this to set our location to a different value than the one stored

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‫in the my vector.

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‫Let's dive in.

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‫So up until this point, we have been dealing with variables that belong to a class.

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‫We've done this in Blueprint and now we've done it in C++.

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‫And this means that the variable is alive for as long as the instance of the class.

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‫Each instance gets its own copy of a variable, but while the class instance is alive, the variable

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‫is two.

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‫Now, this concept that I've just talked about is actually got a name.

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‫It's called Scope.

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‫What it means is how long does the variable live?

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‫And I've just described an instance variable that's a variable that lives as long as a particular instance

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‫of a class.

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‫Now there are other types of variables as well.

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‫There are variables that live as long as a function.

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‫Basically when you call a particular function, that function runs and as soon as the function finishes,

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‫the variable dies.

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‫So in C++, generally speaking, a variable is a valid between the braces in the syntax.

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‫So it's a good rule of thumb.

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‫It's not always exactly correct, but the tick function, for example, we've got some braces here and

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‫if we were to declare a variable inside this tick function, then it would only exist for one time.

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‫The tick function is called and the next time it would be created afresh.

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‫The moving platform.

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‫We can see that if we have a look at the moving platform.

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‫H You can see the my vector is being declared within some curly braces that belong to the definition

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‫of the class, which is why these variables live for as long as an instance of the class does.

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‫So I'd like to prove this to you.

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‫So let's go into the moving platform DHCP and let's create a local variable within this.

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‫So I'm going to create it in exactly the same way as we did.

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‫When we're declaring error in the header file, we're going to have an F vector, then the name of the

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‫vector, I'm going to call it local vector.

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‫And then we can set this a value right when we create it.

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‫We can do that using the constructor for F vector, or we can do it from another variable, just like

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‫we can pass a variable into a function.

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‫So we can first of all use the constructor method.

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‫So we're going to have F vector and I'm going to give it a 1 to 3 and then semicolon at the end of the

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‫line.

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‫So that now is a local variable.

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‫It only exists within this function and it gets reset every single time the function is called.

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‫So if I were to do something like this, if I were to do something like we have on line 29 with the

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‫my vector being updated, we can have a local vector, we can have local vector z is equal to local

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‫vector dot z plus one.

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‫And if I were to set my location to that local vector, it is going to be the same every single frame

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‫because we reset and start from the same location.

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‫One, two, three, every single tick function.

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‫So this function really only exists locally.

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‫So I'd like you to try a little experiment as your challenge to set local vector from the my vector.

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‫So you're going to basically do rather than setting it from the constructor, you're going to set it

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‫from the value that's currently in my vector.

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‫It's going to take a copy of that vector into your local vector.

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‫Then I'd like you to set it to location using the local vector.

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‫And because we're trying to update that local vector every frame, let's see what the effect is.

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‫Does the platform move?

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‫Would you expect it to and go and try it out, compile the code play and see whether it actually does.

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‫Pause the video and have a go.

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‫Okay.

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‫Welcome back.

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‫So I'm going to instead of using the constructor here to set the local vector, I'm going to set my

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‫vector instead.

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‫So we're taking the value that's currently stored in my vector and we're putting it into local vector

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‫and then we are updating the local vector.

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‫We're increasing its said by one every single frame and then I'd like to set actor location instead

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‫of from my vector, we're going to set it from the local vector instead.

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‫Now what's going to happen in this case, do you reckon?

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‫Let's go ahead and find out.

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‫I'm going to hit the compile button and going to go ahead and hit play and we'll see that the platform

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‫is still moving off to the right, but it isn't going up in the Z direction.

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‫So you can see that this isn't really having an impact, the increasing of the local vector because

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‫it's being reset from the current value in my vector, every frame.

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‫My vector, however, is still being updated.

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‫Every frame the y value is being increased, every frame.

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‫And that's why we're seeing the movement over to the right.

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‫So one way we can see that this change to local vector is just local is by increasing this value from

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‫one to maybe 100.

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‫So we're adding 100 to the local vector value.

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‫We can go over and compile and then hit play.

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‫And what you're going to see is that the platform's actually 100 units higher in the air.

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‫Let's just take a second here and eject out with F eight and pause the game with the pause button in

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‫the main toolbar and then select our moving platform to have a look at it in the details pane.

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‫To do that, I'm having to actually click on it in the viewport for some reason.

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‫Sometimes it doesn't work, just clicking on it in the outline.

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‫And I'd like to point out to you that the value in my vector, the z value in my vector is 100 units

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‫less than the Z location of the transform.

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‫So you can see that adding to that local vector has had an impact.

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‫We have got a location, 100 units higher than the location in the my vector.

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‫And what's really great about local variables is that when the function has finished its particular

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‫execution, they get cleared up and reset.

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‫So you can always know what to expect with a local variable.

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‫You always know what value is going to be in it, unlike a class variable which can be updated any time

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‫from any other function.

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‫So we're going to be putting these local variables through their paces in a few lectures time.

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‫Let's dive on.