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Ruby methods have a return value, a value they send back to the code that called them. Let's experiment with return values.
- Ruby methods have a return value, a value they send back to the code that called them.
def add(first, second)
return first + second
end
def subtract(first, second)
return first - second
end
total = add(1, 2)
puts total
remaining = subtract(8, 3)
puts remaining
- We don't need the
returnkeywords here - the last expression evaluated in a method becomes that method's return value.
def add(first, second)
first + second
end
def subtract(first, second)
first - second
end
total = add(1, 2)
puts total
remaining = subtract(8, 3)
puts remaining
- Pass return values to other functions
# We don't have to assign the return value to a variable first.
# We can just pass it straight to "puts".
puts add(1, 2)
puts subtract(8, 3)
# We can also use method return values as arguments to our own methods.
puts add(add(1, 2), 4)
puts add(3, subtract(11, 7))
puts add(add(1, 2), subtract(11, 7))
Returning a value vs. using puts
- It's important to distinguish between method output using
putsand a method return value. - This works because
subtractreturns the result of the subtraction:
def subtract(first, second)
first - second
end
number = 9
puts number # 9
number = subtract(number, 1)
puts number # 8
number = subtract(number, 1)
puts number # 7
- This doesn't work because
subtractreturns the result of callingputs, which is an empty value:
def subtract(first, second)
puts first - second # Returns an empty value!
end
number = 9
puts number # 9
number = subtract(number, 1) # Assigns empty value to "number"!
puts number # Prints empty value!
number = subtract(number, 1) # Tries to subtract from empty value, resulting in error!
puts number # Never runs because of the error!
Widget store code
Here's our widget store code, with the ask method updated to return what the user types.
def ask(question)
print question
# "gets" returns a string the user types.
# Because the call to "gets" is the last
# expression in the "ask" method, the
# return value of "gets" becomes the
# return value of "ask".
gets
end
puts "Welcome to the widget store!"
answer = ask("How many widgets are you ordering?")
puts answer # Prints whatever the user typed.
Additional practice
We've created a workshop where you can get additional practice defining Ruby methods. Don't miss this chance to strengthen your skills; it will make later stages easier!
Visit the workshop here: Practice Ruby Methods
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Let's get back to our
Widget Store program.
0:00
We're still working on asking the user
how many widgets they want to order and
0:02
storing the number they enter.
0:05
Now that we know how to write methods and
pass arguments to them,
0:07
we know most of what we
need to add this feature.
0:11
Let's give it a try now.
0:13
We'll define a new ask
method that takes a question
0:14
parameter in the form of a string.
0:19
Make sure to type an end keyword
to end your method definition.
0:22
And for now let's simply call the print
method within the ask method body and
0:27
pass it the question,
we got as a parameter.
0:34
And following our welcome
to the widget store method,
0:38
let's make a call to this new ask method.
0:41
We'll call ask and then here in
parentheses we'll pass a string.
0:44
And in that string, we'll say,
how many widgets are you ordering?
0:49
Let's save that and
try running it with ruby widgets.rb.
0:59
And we can see our output
down here in the terminal.
1:04
As before we've got our welcome
message welcome at the widget store.
1:07
And then here's the results of our
call to the ask method up here.
1:11
We pass it the string how many
widgets are you ordering?
1:15
And that gets printed down here.
1:18
Notice that it's not skipping to a new
line after printing the question that's
1:20
because we're calling the print
method instead of put S method.
1:24
The reason for
that will become clear shortly.
1:27
Now we need to get the text that
the user enters at the keyboard,
1:29
the gets method can do that for us.
1:34
When we call gets it waits for
the user to type something and
1:36
press enter and
then returns what the user types.
1:40
In this version of ask,
1:43
we'll just assign the value the user
typed to a variable answer.
1:45
We'll name our variable answer and we'll
assign it the return value from gets.
1:50
And then we'll simply print that value.
1:55
So we'll save that and try running it.
2:01
And as before, it'll print out
the question that it's asking us.
2:03
How many widgets are you ordering?
2:09
And now it's waiting for
us to type some input in the keyboard.
2:11
And that's why we used a print method to
print the question instead of puts which
2:14
would skip down to the next line.
2:19
Our input is going to appear here
on the same line as the question.
2:20
So now we can type whatever
we want here at the prompt.
2:25
So I'll use a value of 8 and
press Enter when I'm done.
2:28
And the value that I typed will
get returned from the gets method,
2:32
assigned to the answer variable,
and then that will get passed to
2:37
the puts method called down here,
and printed out to the console.
2:41
So we typed 8, and it prints 8.
2:45
So how does this work exactly?
2:49
Well, Ruby methods have a return value,
2:51
a value that they send back
to the code that called them.
2:53
Here, the return value from gets is
getting assigned to the variable answer.
2:56
Let's take a look at return
values in another context though.
3:02
Here are our add and
subtract methods from before.
3:05
First I'm going to get rid of this first
line here, which prints out the parameters
3:08
that they receive cuz we don't
really need that code anymore.
3:13
Now currently the add and subtract methods
just print the result of adding or
3:16
subtracting their first and
second parameters.
3:21
But let's modify these methods so
that they use a return value instead.
3:24
I'm going to remove the call to puts and
then in its place,
3:28
I'm going to use the return keyword.
3:32
Following the return keyword is
an argument that you want to
3:36
return to the method caller.
3:40
So in this case, we'll just use the exact
same code that we did previously.
3:43
We'll add the first and
second parameters and return that value.
3:47
Down here I'll remove the call to puts and
I'll use a return keyword there as well.
3:50
Let's try running this.
3:56
Ruby parameters.rb and we don't get
any output right at first that's
4:02
because the return keyword
doesn't print a value or
4:07
do anything besides pass it back
to the code that called it.
4:11
In order to actually see the output again
we're going to need to do something with
4:15
those return values down here in the place
that we're calling these methods.
4:19
So this call to the add method here is
actually returning a value right now.
4:24
It's calling the result of adding
its first and second parameters.
4:28
But we're not actually doing
anything with that return value.
4:32
So I'm going to take the return value and
pass it to puts method down here.
4:35
If we save that and try running it,
4:40
this time we'll see output.
4:42
We'll see the return value that we're
getting from the add function, 150.
4:45
Let's do the same for
the remaining method calls.
4:49
So puts subtract, puts add, puts subtract.
4:51
Try running it again.
4:57
And this time you can see that all four of
our method calls are returning values and
4:59
then we're printing them out down here.
5:04
We don't actually need
the return keywords here though.
5:07
The last expression evaluated in a method
becomes that method's return value.
5:10
So if we were to remove the return
keyword here, first plus second would be
5:15
the last expression evaluated
within the add method's body, and
5:20
that would become the
method's return value.
5:24
So let's remove the return
keyword from add, and
5:27
we can remove the return
keyword from subtract as well
5:30
because this expression will be the return
value of the subtract method.
5:33
And if we try running this, it'll behave
in just the same way it did before.
5:37
There's a variety of things you
can do with Ruby return values.
5:44
You can either take the return value and
pass it directly to another
5:48
method as we're doing with puts in
our add and subtract methods here.
5:51
Or you can assign a return value to
a variable first, if you prefer.
5:55
So for example, we can assign
the return value from add here to
5:59
a total variable, and
then print that out if we want.
6:04
Save that, try running it.
6:08
And you can see that the end
result is the same here.
6:09
We take our first call to add.
6:13
Its return value is going to be 150.
6:16
We assign that to the total variable and
then print that out here.
6:18
And you can see a 150 in
our results down here.
6:21
We can also use method return values
as arguments for our own methods.
6:24
So for example, I can take the return
value from calling add 1 and
6:29
2, and I can pass that back to
the add method as an argument.
6:34
So add 1 and 2 will give us three,
we can add 3 and 4 like this.
6:39
Let's try saving that, and running it.
6:46
Whoops, I forgot to call
puts with that return value.
6:52
Let me go back up into the code and
have that there.
6:54
And that's we had no output.
6:56
Let's see if we get output this time.
6:58
There we go.
6:59
The result of adding 1 and 2 is 3, and
the result of adding that to 4 is 7.
7:01
You can see that in the output down here.
7:07
Let's try making another call to add.
7:09
And this time we'll take the number 3 and
we'll add the results of subtracting.
7:12
11 and 7,
7:22
try running that.
7:26
And the results of subtracting 7
from 11 is 4 if we add that to 3,
7:30
the result is 7 again.
7:36
It's very important not to confuse
a method returning a value
7:38
with if printing a value using puts.
7:43
So let's take our subtract method
here and let's pass a variable to it.
7:45
We'll declare a variable named number and
we'll assign it a value of 9.
7:50
We'll print out of the value it contains.
7:55
And then we'll reassign to that variable
the result of calling the subtract method.
7:58
A little typo there, let me correct that.
8:10
And we'll call the subtract method
with the value currently in number.
8:12
And the number 1, which will subtract
1 from whatever's in number and
8:16
assign that back to number.
8:22
So number should contain 8 after this,
and let's copy and
8:25
paste that code so
that we do it again a second time.
8:29
And then with printing the final
value in the number variable.
8:33
Okay, let's try running this.
8:37
And we see 9, 8, 7 as our output.
8:42
We start with 9, subtract 1 and
get 8, subtract 1 again and get 7.
8:45
But suppose that instead of returning
a value, the subtract method
8:49
printed the result of subtracting
its second argument from its first.
8:53
This will actually return an empty
value from the subtract method.
8:57
So lets try running this, and
it appears to work correctly at first.
9:02
It prints out the value and
our number variable 9, and
9:07
then it appears to subtract 1 from it
giving us 8 and printing that out.
9:10
But what's actually happening here,
9:14
is that the call to puts is
returning an empty value.
9:16
And that's what gets assigned to
the number variable down here.
9:19
Then when we try to call subtract with
number, which now contains this empty
9:22
value, we get an undefined method minus
for NilClass, that is an empty value.
9:28
So make sure not to confuse a method
calling puts with returning a value.
9:33
In many cases a method will only work
correctly if it actually returns a value.
9:38
So now that we actually understand
method return values a bit better,
9:43
let's update our ask method to use them.
9:47
Instead of taking the value
return from gets and
9:50
assigning it to a variable and
then printing that variable out,
9:53
let's simply return the user's
input from the ask method.
9:57
We'll assign that return value to
a variable named answer down here.
10:00
And then after that we'll print the value
that the answer variable holds.
10:06
This way we'll be able to do other
things with the user's response out
10:10
here in the main code.
10:15
Let's save then and try running it.
10:17
Ruby widets.rb and it'll ask us
how many widgets are you ordering?
10:22
Let's say 8.
10:26
And as before it will print
the value that we input of 8.
10:27
We've completed the second feature for
our program.
10:33
We ask the user which quantity of widgets
they want, call the gets method to get
10:36
their keyboard entry, and store
the return value from gets in a variable.
10:41
Learning the call methods was the key
to getting this far in your program.
10:45
Practicing your new skills is
important to making them stick.
10:49
So be sure to check the teacher's notes
on this video for some practice ideas.
10:53
You're off to a great start learning Ruby.
10:57
You've learned the call methods and
to use their return values.
11:00
You've even learned to
write your own methods.
11:03
Those skills would be useful in
pretty much every program you write.
11:05
And now, you can also store values
in variables when you need to,
11:10
that's another skill
you'll be using a lot.
11:13
There's just one minor
issue with the program.
11:16
When we ask the user how many
widgets they want to buy,
11:19
our question runs right up against
the place their keyboard input is shown.
11:22
That looks a little
less than professional.
11:26
To fix this, we're going to need
to learn more about strings.
11:29
Just like most other
programming languages,
11:33
Ruby uses strings to store text.
11:36
We'll learn all about
them in the next stage.
11:38
See you there.
11:41
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