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And this lecture we're going to talk about variables and mutability.

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Variables are how we are going to store the data that is necessary for our application to run.

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And then mutability is going to refer to how.

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That data can be manipulated.

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If it's mutable, we are able to modify the variable, but if it's in mutable, we will not be allowed

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to modify it.

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So to demonstrate this, we're going to create a new directory called Variables Using Cargo, and we're

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going to change into that directory.

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So now if we look at the folder structure.

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It is the same as what we're used to, especially with Helo.

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So we'll go into main hours and we will delete.

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That line.

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So the first thing that we're going to do is use the keyword.

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And this is basically saying, hey, this is going to be a variable.

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So we're going to say let X equal five and then we're going to use the print line macro, which is going

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to allow us to print information out to the terminal.

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We'll cover macros more in depth later on.

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But for now, just know that print line with the exclamation point is how you print information out

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to the terminal.

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So we will say.

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The value of x is and then curly brackets.

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And specify the variable that we want to print out.

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Also if you're not super familiar with Visual Studio code.

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If you click file and go down to AutoSave, it'll automatically save for you.

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That way, you don't have to continuously do it.

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Now, if we run cargo build and cargo run, we get the desired output of the value of x is five.

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So now what happens if we try to assign?

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Six to the variable x and then print out the same.

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So we will build it again and we get an air.

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So if we bring this up.

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We can see that the air says cannot assign twice to immutable variable x and it'll tell us that.

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At line two, we first assigned to X and then at line six we're trying to reassign to X, but it also

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says considered making this binding mutable.

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So if we come up here and put.

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Cute.

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X our air for that squiggly that was that line six.

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So just so you can see it again how it's how it has it here.

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So now if we put mute that air is now gone.

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So if we build it again and then run, we now have the desired output.

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So what this is keyword right here is doing is it's allowing us to be able to modify the X variable.

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So that's really important to know because if you forget that mute keyword, then you're not allowed

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to modify any variables.

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Another keyword that we can use to make sure variables are not able to be modified is const.

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Konst is going to allow the variable to live as long as the program is alive.

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So what we'll do is we'll create a count called seconds and we'll assign it the data type of eight.

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And I'll get into data types in the next lecture.

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Now by Russia's naming convention.

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Constants are always going to be in all capital letters.

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So any time you see a variable in all caps, it should be a concert by naming convention.

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So what we'll do here is we'll print out again.

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The value of seconds is seconds and we will cargo build, cargo run and we see the value of seconds

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is 60.

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So constants cannot.

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B mutated at all.

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So as you can see, it's already complaining about it.

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Cons globals cannot be mutable.

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So luckily Russ is really friendly with telling us all of this information, but it's all very important.

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Beginner steps on knowing how to instantiate a variable.

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So in the next lecture we will talk about data types.