The functions in the previous exercises produced output via println() statements contained within its code body; however, we also have the ability to return a value from a function.

A return statement returns a value from a function and passes it back to where the function was invoked. This value can then be used throughout our program.

If we want a function to return a value, we must add the return type to the function header as well as a return statement in the body. Take a look at the following example where we create a function that takes in a list of Ints and returns an Int value:

fun listSum(myList: List<Int>): Int {
  var sum = 0
  // iterate through each value and add it to sum
  for (i in myList) {
    sum += i
  }
  // return statement
  return sum
}

• The return type describes the data type of the value being returned and is stated after the parentheses and a colon : in the function header.
• The keyword return is used to declare a return statement. In this case, sum is the value being returned.
• Any lines of code that exist after the return statement will not be executed.

Previously, we invoked functions by calling them on their own line of code; however, we can also invoke a function and assign it to a variable for later use.

For example, we can set total to the return value of listSum() after sending it a list of Int values (billsToPay):

var billsToPay = mutableListOf(44, 29, 104, 79)

// Set total to the return value of listSum().
var total = listSum(billsToPay)
println("Your bill total is $total dollars.")

This will output the following:

Your bill total is 256 dollars.