Ruby Loops

5:19 with Jason Seifer

A loop is a piece of code that will run the statements inside until some condition is met. We can use loops to do things like asking a user if they want to keep entering input until they type "done" or "no" or something similar. There are several different kinds of loops available in Ruby. We can write a loop using the "loop" keyword.

Teacher's Notes
Video Transcript
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Important!

We create an infinite loop when writing code in this lesson. To exit the loop, hold the Ctrl key and press C. On Windows, you can also use Ctrl + Pause/Break.

Terms

Infinite Loop: A loop that never exits.

Code Samples

Here is our simple loop:

loop do
  print "Do you want to continue? (y/n) "
  answer = gets.chomp.downcase
end

The above code creates an infinite loop, or, a loop that never exits. To fix that, we can use the break keyword to exit the loop.

loop do
  print "Do you want to continue? (y/n) "
  answer = gets.chomp.downcase
  if answer == "n"
    break
  end
end

[MUSIC] 0:00 Hi I'm Jason, a Ruby developer. 0:04 In this course we're going to look at loops and iteration in Ruby. 0:07 So far when we've been writing our programs and 0:11 want to do something more than one time we've written those things out. 0:14 In the Ruby Collections course, when we were adding items to our grocery list, we 0:19 wrote a method called add list item, which added a new item to our grocery list. 0:24 But this tedious and computers are really good at doing things for us. 0:30 Another way we could have written that program is using something called a Loop. 0:36 A loop is a piece of code that will run the statements inside 0:41 until some condition is met. 0:45 Using the grocery list example, we could have a loop ask a user if they wanna keep 0:48 entering grocery list items until they type done, or no, or something similar. 0:53 There are several different kinds of loops available in Ruby. 1:00 We can write a loop using the loop keyword. 1:04 Let's see how that works now using workspaces. 1:08 Okay, so I have just launched a new Ruby workspace. 1:12 If you see the welcome document, you can go ahead and close it. 1:16 Now let's go ahead and create a new file. 1:21 And we'll call this loop.rb. 1:25 In order to create a loop, we use the loop keyword followed by the word do. 1:30 And then, we close this, by typing end. 1:39 Now, whatever is inside, what is called a block here, 1:44 between the do and end, will be run, until we tell it to stop. 1:49 So let's go ahead and just print something out here. 1:55 We'll just say, do you want to continue? 2:01 And then we'll get the answer. 2:07 Now I've saved the file and let's click down here 2:13 into the console area and run this by typing ruby loop.rb. 2:18 Now we see this asks do we want to continue. 2:27 And I will type y. 2:30 Actually, we can type anything we want here. 2:33 And this is going to continue forever. 2:36 Because we haven't told it to do anything, or given it any way to exit the loop. 2:40 We can stop this loop by holding the Ctrl+C. 2:45 That will give us this message saying that it has been interrupted. 2:50 Don't worry about that. 2:56 Ctrl+C is going to cancel the currently running program, or 2:57 in this case, interrupt it. 3:02 You'll notice that this loop goes on forever. 3:05 This is something called an Infinite Loop. 3:08 An infinite loop occurs when there's no condition to exit the loop, 3:12 or the condition that would exit the loop can never be met. 3:17 Let's modify the loops so that it has a way to exit. 3:22 When we look back up here, we see loop, and then do, and end. 3:25 Do and end is something called a block in Ruby. 3:31 Blocks are written one of two ways, using either the do and end keywords. 3:35 You can also use curly braces. 3:41 And if we run this again, we should see the same thing. 3:47 I'm gonna clear my screen here by holding the Ctrl+L. 3:50 And we see if we continue, we get the same thing. 3:59 And once again, I'm going to press Ctrl+C to exit. 4:04 And I'm going to change this back from curly braces to do and end. 4:09 Blocks can be written either way, with curly braces or 4:16 with the do and end key words. 4:19 By convention, most Ruby programmers will use do and 4:22 end if the statements inside the block take up more than one line of code. 4:25 If it only takes up one line of code, it's convention to use the curly braces. 4:30 So let's go ahead and fix this infinite loop here. 4:37 And we'll actually do something with the answer. 4:40 We'll say if the answer is a lower case 4:43 n, then we need to exit this loop somehow. 4:49 We can do that using the break keyword, 4:56 which will break us out of the current loop. 4:59 I'm gonna run this again. 5:04 Let me clear my screen here. 5:05 And if I type ruby loop.rb. 5:07 Do you want to continue? 5:10 Yes. 5:11 Do you want to continue? 5:12 No. 5:14 And that exits the loop and also the program. 5:15

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