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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 0:45 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, 1:02 multiply the whole thing by 2, 1:07 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, 1:19 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 1:33 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. 2:06 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 2:21 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 2:41 of a Ruby method becomes the return value of that method. 2:45 So we can actually take the return keyword off here. 2:49 Length times width will be the last expression we evaluate within the area 2:53 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, 3:03 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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