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Your goal was to build a simple Ruby program that calculates the area and perimeter of a rectangle. Here's our solution.

#### Extra credit

- Write a method that accepts the length, width, and height of a box, and returns its volume (
`length * width * height`

). - Write a method that accepts the radius of a circle, and returns its area (
`Math::PI * radius ** 2`

).

Your goal was to build a simple Ruby
program that calculates the area and
0:00

perimeter of a rectangle.
0:03

Here's my solution.
0:05

It's okay if yours is slightly different.
0:07

But if you see something
interesting in my code,
0:09

you should consider borrowing it
to improve your own own program.
0:11

So up here I have defined an area method.
0:15

And it takes two parameters,
a length and a width.
0:17

And that's all that we need to
calculate an area for a rectangle.
0:22

We just multiply the length by the width,
store that in a variable, and
0:26

then return that variable.
0:31

Next step, we were supposed
to define a perimeter method.
0:35

Which, if you visualize a rectangle,
there are two sides where the length is
0:38

the same and
two sides where the width is the same.
0:42

So you just add the length and
the width together and
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multiply the whole thing by two.
0:48

Making sure to complete the addition
operation before doing the multiplication.
0:50

You can use parentheses to ensure that
the correct order of operations is
0:55

followed there.
0:59

So we just accept length and
width parameters, add those together,
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multiply the whole thing by 2,
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assign that to a variable, and
return the value of that variable.
1:09

Then down here we were supposed to
call the methods that we've created.
1:14

So we make a call to the area method,
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we pass it a length and
a width as arguments.
1:22

And here we make a call to perimeter,
again passing a length and
1:27

a width as arguments.
1:31

We take the return values of
each of those methods and
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pass those in turn to the puts method
which just prints those values out.
1:37

So we make a call here to area,
with a length of 2 and a width of 4.
1:42

It multiplies those two together and
we get a resulting area of 8.
1:47

Here, we make a call to perimeter,
with a length of 2 and a width of 4.
1:52

It adds the length and
width together, giving us 6, and
1:56

then multiplies the result by 2,
giving us a return value of 12.
1:58

Now this is one way to do it but this is
actually a little longer than necessary.
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It's not Idiomatic Ruby.
2:10

We can shorten this up by simply returning
2:12

the result of the math operations.
2:16

So we can get rid of the variable
that we're storing everything in, and
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just return the results
of the math operation.
2:25

Let's try saving this and
running it again.
2:30

And you see we get the same results.
2:33

But we can actually make
it even shorter than that.
2:38

The last expression that gets
evaluated within the body
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of a Ruby method becomes
the return value of that method.
2:45

So we can actually take
the return keyword off here.
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Length times width will be the last
expression we evaluate within the area
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method, and so this will return the length
and the width that were passed in.
2:57

We can do the same down here in perimeter,
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the last expression that we evaluate
here is 2 times length plus width.
3:05

And that just becomes the return
value of the perimeter method.
3:10

So let's save this, try running it again.
3:14

And again we get the same result.
3:18

This is a much more succinct
way to write methods in Ruby.
3:20

And if your methods are short,
3:24

you should consider leaving off
the return keyword altogether.
3:25

I hope you got in some good Ruby practice.
3:30

See the teacher's notes for
some other experiments you might try.
3:32

Have fun!
3:35

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