Programonic

Before you start

Kotlin basics.

Declare typed parameters and a return type.
Predict the sample output and explain the state changes.
Complete the practice task and check the boundary cases.

The concept

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.

Code example

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

Example details

Follow the code

Open the walkthrough to inspect the example one step at a time.

Show guided walkthrough

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

Behind the scenes

How Kotlin processes this code

Kotlin commonly compiles to JVM bytecode, which the JVM executes.

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