WEBVTT

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[MUSIC]

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Hi I'm Jason, a Ruby developer.

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In this course we're going to look
at loops and iteration in Ruby.

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So far when we've been
writing our programs and

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want to do something more than one
time we've written those things out.

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In the Ruby Collections course, when we
were adding items to our grocery list, we

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wrote a method called add list item, which
added a new item to our grocery list.

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But this tedious and computers
are really good at doing things for us.

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Another way we could have written that
program is using something called a Loop.

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A loop is a piece of code that
will run the statements inside

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until some condition is met.

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Using the grocery list example, we could
have a loop ask a user if they wanna keep

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entering grocery list items until they
type done, or no, or something similar.

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There are several different kinds
of loops available in Ruby.

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We can write a loop
using the loop keyword.

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Let's see how that works
now using workspaces.

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Okay, so
I have just launched a new Ruby workspace.

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If you see the welcome document,
you can go ahead and close it.

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Now let's go ahead and create a new file.

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And we'll call this loop.rb.

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In order to create a loop, we use
the loop keyword followed by the word do.

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And then, we close this, by typing end.

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Now, whatever is inside,
what is called a block here,

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between the do and end, will be run,
until we tell it to stop.

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So let's go ahead and
just print something out here.

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We'll just say, do you want to continue?

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And then we'll get the answer.

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Now I've saved the file and
let's click down here

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into the console area and
run this by typing ruby loop.rb.

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Now we see this asks do
we want to continue.

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And I will type y.

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Actually, we can type
anything we want here.

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And this is going to continue forever.

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Because we haven't told it to do anything,
or given it any way to exit the loop.

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We can stop this loop
by holding the Ctrl+C.

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That will give us this message
saying that it has been interrupted.

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Don't worry about that.

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Ctrl+C is going to cancel
the currently running program, or

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in this case, interrupt it.

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You'll notice that this
loop goes on forever.

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This is something called an Infinite Loop.

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An infinite loop occurs when there's
no condition to exit the loop,

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or the condition that would
exit the loop can never be met.

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Let's modify the loops so
that it has a way to exit.

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When we look back up here,
we see loop, and then do, and end.

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Do and
end is something called a block in Ruby.

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Blocks are written one of two ways,
using either the do and end keywords.

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You can also use curly braces.

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And if we run this again,
we should see the same thing.

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I'm gonna clear my screen
here by holding the Ctrl+L.

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And we see if we continue,
we get the same thing.

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And once again,
I'm going to press Ctrl+C to exit.

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And I'm going to change this back
from curly braces to do and end.

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Blocks can be written either way,
with curly braces or

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with the do and end key words.

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By convention,
most Ruby programmers will use do and

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end if the statements inside the block
take up more than one line of code.

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If it only takes up one line of code,
it's convention to use the curly braces.

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So let's go ahead and
fix this infinite loop here.

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And we'll actually do
something with the answer.

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We'll say if the answer is a lower case

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n, then we need to exit this loop somehow.

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We can do that using the break keyword,

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which will break us out
of the current loop.

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I'm gonna run this again.

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Let me clear my screen here.

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And if I type ruby loop.rb.

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Do you want to continue?

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Yes.

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Do you want to continue?

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No.

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And that exits the loop and
also the program.