Kotlin Functions

Declare typed parameters and a return type.

Kotlin

fun average(values: List<Int>): Double {
    return values.sum().toDouble() / values.size
}

fun main() {
    println(average(listOf(82, 91, 76, 95)))
}

Output

86.0

Explanation

A Kotlin function starts with fun, lists parameters as name: Type, and declares its return type after a colon. Types are required for parameters.

values.sum() adds the integers. Converting to Double before dividing matters, because dividing two Ints in Kotlin discards the fraction. The result 344 / 4 prints as 86.0 because the value is a Double.

Explore the dry run

Guided walkthroughReady

1fun average(values: List<Int>): Double {

2 return values.sum().toDouble() / values.size

3}

5fun main() {

6 println(average(listOf(82, 91, 76, 95)))

7}

Follow the example

Start to inspect the source, values, and output. These prepared steps explain the published sample; grouped loop steps describe multiple iterations.

View the complete dry-run table

Prepared trace of the published program. Some rows group repeated iterations.
What happens	State after step	Output so far
Take a list of ints and promise a Double.	`—`	—
344 as a Double divided by 4.	`return = 86.0`	—
Print the returned Double.	`return = 86.0`	86.0

Cost and common mistakes

O(n) time and O(1) extra space.

Without converting to Double, 344 / 4 would use integer division and lose any remainder.
average(emptyList()) would divide by zero and give NaN for Doubles; check for an empty list first.

Try it yourself

Predict average(listOf(1, 2)).

Reveal answer and reasoning

The sum is 3, and 3.0 / 2 is 1.5.

Kotlin Functions

Explanation

Follow the example

Cost and common mistakes

Try it yourself

Further reading