Functions and Return Values
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Similar to how functions can take in values as parameters, functions can also return values.
Recall the addTen
function from the previous chapter:
This function takes in a parameter, x
, and adds 10 to it. Lastly, the program prints the value to the console.
But what if we wanted to store the value of x
plus 10? In the function above, x + 10
is stored into a local variable called xPlusTen
. However, this variable is lost when the function is finished -- it cannot be accessed outside of the function.
Using a return statement will allow us to pass a value back out of the function. That return value can be stored into a variable for later use.
Here's how to rewrite addTen
to return a value instead of printing:
Note that the return
keyword does not require parentheses. Also, returning a value does not print that value to the console, similar to how passing in a value as a parameter does not print the value to the console.
A return value by itself would not be very useful, given that it does not print to the console. Fortunately, we can store a function's return value into a variable. Take a look at the following code:
First, we create a variable named num
and initialize it to 7. Then, we create another variable called tenAdded
. Notice that tenAdded
is not given a normal value. Instead, we are setting it equal to addTen(7)
. This means that the tenAdded
variable will hold the result of whatever the function call addTen(7)
returns. We know that addTen(7)
will return 17, so tenAdded
will be 17
.
Return values work in many situations. For example, we can rewrite the add
function from the previous section to return the sum instead of print it to the screen:
We can now call the function and store its return values
which would print 100
to the console.