Back in our temp.rb file, our wait method always waits three seconds.

What if we wanted to be able to specify how long it should wait for?

Puts and print both take text that they want displayed.

Sleep takes a number of seconds to sleep for, but how are they doing that?

Before we can answer that we need to explain variables.

Variables aren't a complex concept but they're fundamental to programming.

You probably remember working with variables in your Algebra class.

They were often denoted with with an X or a Y and

were used to hold a variety of possible values.

That is, variables are names for values that can vary.

In this equation Y = X + 5, if we set X equal to 1, then Y would equal 6.

If we set X equal to 10, then Y would equal 15, and so on.

Variables in a programming language are like that, but

they can hold other things besides numbers.

They can hold texts or a calendar date, or

any other piece of data that can be stored in your computer's memory.

Let's create a new Ruby source file so

we can play around with variables a little bit.

I'll click on the file menu, choose New File, and

I'll type the name of variables.rb.

When you assign a value to a variable,

you're giving that value a name that you can refer to it by.

You assign a value to a variable with single equal sign.

So, let's create a new variable named number and

assign a value to it with =, and we'll give it a value of 4.

Then we'll create another variable named greeting, and

we'll assign a value to that with equals.

And this one, we're going to assign a string value to.

So we open our string with a quotation mark.

We'll make the string say hello.

And we'll end the string with another quotation mark.

We can then use that variable anywhere we might use the original piece of data.

So let's try making a call to puts to print a value out.

And instead of passing puts the number 4, I'm going to pass it the variable number.

Let's try saving that and running it.

Down here in the console I will type ruby,

space, and then our new source code file name, variables.rb.

And you can see that it prints out the number 4.

It prints out the value that the variable number holds.

Let's try doing the same with the greeting variable.

We'll call it the puts method, and

as an argument we'll pass it the variable greeting.

Save that and try running it again.

And first it will print the value of number followed by the value of greeting.

We can even use variables within other expressions.

Let's make another call to puts, and

this time we'll pass it the result of adding 2 to the value in number.

Save that, try running it.

And you see that first it prints the original value of number four,

then the value of greeting, hello, and

then it prints the value resulting from adding 2 to the value in number.

You get 6 as a result.

It's worth noting that math operations like this don't affect the value

that's in the variable, unless you assign that new value back to the variable.

So if we were to call puts again here and

pass number to it and try running that again.

You'll see that the original value held in number is 4,

we add 2 to it and print that out here and get the result 6.

But you can see that the value contained within the number variable hasn't changed,

it's still 4 and that's what gets printed last.

Let's do one more operation with the value and

number we'll subtract, 12 minus number.

Try saving that.

Run it.

And you can see that it finally prints the value 8 because number still holds 4,

and 12 minus 4 is 8.

If we change the value that a variable holds,

the remainder of the program will use that new value instead of the old one.

So let's try changing the value and number to 6 here at the top of the program, and

we'll try changing the string in the greeting variable from hello to hi.

Try running that.

And you can see the results reflected in the output here,

it prints out the value in number which is now 6 instead of four.

It prints out the value of your greeting which is now hi, instead of hello.

Number plus 2 is now 8 because 6 plus 2 is 8.

And 12 minus number is 6 because number still holds 6.

We can even replace the value a variable holds in the middle of a program.

So here after number plus 2, let's try assigning a new value to number.

We'll say number equals 10.

Try running that.

And you'll see that the program starts

printing 6, because that's the value that number holds at first.

And here it prints 8, because 6 plus 2 is 8.

But here we changed the value to 10.

And so, 12 minus 10 gives us a result of 2.

We were able to change the value that our number variable held

in the middle of our program.