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Before we look at functions in more
detail, we're going now to take a few

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minutes to see what happens when you
call a function. You've probably worked

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out that execution will jump to line two,
when we call the multiply function,

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so let's see that happening. What I'm going
to do is set a breakpoint on line six,

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then run the program in the debugger.

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So the debugger stops on line six, where
we call multiply. In an earlier video,

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way back in the Program Flow Control
section, I said that I'd explain about

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the Step into my code button later. It's
now later.

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Up until now, we've been using the Step
over button -

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this one here - so let's start by seeing
what that does. I'm going to click Step

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over, to execute line six.
We get the answer in the console tab,

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and also to the right of line six. So the
Step over button executes a line, without

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stepping into any functions on that line.
So if you restart this again,

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and we stopped on line six again, we want
to make sure that the debugger tab is

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selected. This time, what I'm going to do
is use the Step into my code button - and

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that's not this one here. It's the one to
the right of that, Step into my code.

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Once I click that, notice that this time, the
program execution has jumped to line two.

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We've entered the code in our multiply
function. When you want to check the code

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in your functions, remember to use the
Step into my code button, as I just did.

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Using Step over, will execute the code in
your function without stepping through it.

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The step into button does the same thing

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at the moment - the one to the left of the
button that I clicked. You won't see a

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difference until you start splitting your
code into different modules. But get into

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the habit of using Step into my code,
because that's generally the code that

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you want to debug. Alright, so we're now
on line two,

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inside the multiply function. That's
about to multiply the two numbers,

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and store the result into the variable
called result. So at this point, we can

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either use the Step over, or Step into my
code here. They'll both do the same thing

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when there isn't a function call on the
current line. So as a result, I'm just going

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to use Step over, over here to the left,
just because that's a better description

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of what we're actually doing. We can see
that result now has the value 42.0,

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up there on line two, and we're ready to
execute line three. Before I Step over

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that line, have a look at the variables
in the debugger pane, down the bottom.

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We've got the variable result in there.
Keep an eye on that pane, because I want

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to talk about the scope of variables.
This is a good way to understand scope.

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That variable only exists inside the
multiply function. You'll see it vanish

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when we leave the function, so let's do
that. I'm going to click Step over again,

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and we get back to line 6, as you can see
there now. Notice that result has

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disappeared from the variables pane. Now
that's important - it no longer exists.

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I'm going to come back to this and talk
about scope in more detail, in the next

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video. So we're back on line 6, and the
code in our multiply function has been

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executed. It's returned a value and the
debugger is ready to proceed. When we

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press Step over again, which I'll do now,
line 6 finishes by binding the variable

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answer, to the value returned by our
function. We can now see answer in the

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variables pane, bound to the value 42.0.
Line seven's not very exciting. I'm gonna

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click on Step over again, to print the
value and terminate the program, and

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we can go to the console here, to confirm
the value 42.0 has been printed out.

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Step through this code, though, a few more times,

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until you're happy that you understand
what's happening,

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and I'll see you in the next video.