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Loop Conditionals
7:13A loop conditional will exit a loop. A loop will run forever until the condition to exit the loop returns the value of true. If the condition returns the value of false, the loop will not exit. If the condition never returns true, we'll create an infinite loop.
As we just saw, a loop will run
forever until a condition is met.
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When we say that the condition is met,
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that means that the condition to exit
the loop returns the value of true.
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If the condition returns the value
of false, the loop will not exit.
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If the condition never returns true,
we'll create an infinite loop.
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We've already learned about
Conditionals and Complex Conditionals.
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So feel free to brush up on those using
the course linked below in the notes.
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Let's do a quick review now on writing
conditionals specifically to exit a loop
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using workspaces.
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Using a Ruby workspace,
let's go ahead and create a new file, and
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we're going to call this
loop_conditional.rb.
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So here we go.
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Now let's go ahead and
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make a quick little program to guess
a number between zero and five.
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Now we'll do this by
generating a random number and
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we can do that using the random class and
we'll have a link
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to the documentation right below the video
here in the Teacher Notes section.
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But the way we create a random
number is by typing Random.new.
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And then we can give it an argument
which is the maximum that we want.
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So let's go ahead and create this.
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We'll do a random number here.
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And we do that by saying,
Random.new.rand(5).
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We'll just have a number between zero and
five.
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And then let's create a loop to
make somebody guess the number.
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We'll say Guess the number between 0 and
5 (e to exit).
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And then we will get the answer
from standard input.
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And let's first check to see if
they have entered e to exit.
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So if the answer is e.
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We will break to exit the loop.
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And if not,
we'll see if they guessed correctly.
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Then we'll save the answer and
we'll make this an integer instead.
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We will print to the screen,
You guessed correctly.
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And then we will break and if not,
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we'll print out, Try again.
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And actually, let's go ahead and
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tell them what the number was if
they just simply exit the program.
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Okay, now let's go ahead and run this by
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typing ruby loop_conditional.rb.
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So let's guess the number.
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How about two?
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No.
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Three?
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Uh-oh.
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Four?
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I guessed correctly and it exited.
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We have a bit of a complicated
if statement here.
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The first thing that we check is to
make sure that the answer is not exit,
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and if the answer is an exit,
we'll print out the random number.
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The important part is
using the break statement.
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If we don't break,
then we get in an infinite loop.
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And let's go ahead and
just make sure that works again.
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And e to exit, and
the number was one, okay.
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So, it looks like all of the different
execution paths are working correctly.
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And let's go ahead and
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create another file and just make
sure that it works with numbers too.
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I'm calling this one
loop_conditional_number.
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And let's just ask the user to enter
a number greater than ten to exit.
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And we'll do the same thing, but
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all in one go we'll get
the answer from standard input.
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And then we will exit the loop if
the number is greater than ten.
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And so we can say, if answer is
greater than ten, we will break.
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Let's run that.
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And see what happens,
enter a number greater than ten.
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I entered two, nothing happens.
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I enter 11 and it exits,
which is what we wanted.
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One neat thing about if statements is
that they can be written on one line,
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which can be a little bit more clear
depending on how you're reading the code.
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So if we run this again, we
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can see that it properly exits when we
keep the if statement all on one line.
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Okay, now let's do one more, and
we're gonna call this loop_name.rb.
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I'm actually gonna paste the code in,
and then we'll see how it works.
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So, right here we have got
a method called get_name.
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And what this does is create a variable
called name which is set to an empty
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string.
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Then we loop through,
ask the user to enter their name, and
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then get that from standard input.
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From there, we check to make sure
that the name meets the criteria
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that we've set forth, which is that
it's a minimum of two characters and
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doesn't contain any numbers.
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So if all that checks out,
then we break out of the loop and
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return the name variable
from the get_name method.
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And if that criteria is not met,
we print out a message saying
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that the name must be longer than two
characters and not contain any numbers.
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This right here is a method
called index which uses
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a regular expression to check whether or
not there are any digits in the name.
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We'll have a link below to more
information on regular expressions.
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You don't need to worry about
them too much right now.
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Just know that it checks the name for
any digits.
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Now let's go ahead and
run this and see what happens.
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So I'll click down into the console and
type ruby loop_name.rb.
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Enter my name.
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I'll just put J for Jason, and now it
says that my name must be longer than two
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characters and not contain numbers.
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This is what I was expecting.
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So let's try J2.
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Same message.
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Now if I typed in my name correctly,
it says hi Jason.
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You'll notice that we can use complex
conditionals to break out of loops.
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Try practicing writing some loop
conditionals on your own now
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using workspaces.
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