Defining functions

Learn to define functions with fun.

Defining functions: fun

In Kotlin a function starts with the fun keyword. Parameters are written as name: Type; the body sits inside { }. To call it, write the function name and the arguments in parentheses.

fun greet(name: String) {
    println("Hello $name")
}
greet("Ava")  // Hello Ava

Parameters are separated by commas: fun add(a: Int, b: Int). Type names start with a capital: Int, String, Boolean.

Function call and argument order

To call a defined function, write its name and the arguments in parentheses. Arguments bind to parameters by position: the first argument goes to the first parameter, the second to the second.

fun greet(name: String, msg: String) {
    println("$msg $name")
}
greet("Ava", "Hi")  // Hi Ava

The argument count must match the parameter count; otherwise you get a compile error. This makes the call checked at compile time.

Exercise Define greet and call it

Define a fun greet(name: String) whose body is println("Hello $name"). From main call greet("Ava").

Show example solution

fun main() {
    greet("Ava")
}

fun greet(name: String) {
    println("Hello $name")
}

Test yourself

Fill in the blank: parameter type

fun greet(name: ____) {
    println(name)
}

Show answer

fun greet(name: String) {
    println(name)
}

Which is a valid Kotlin function definition?
- function greet(name: String) { println(name) }
- fun greet(name: String) { println(name) }
- def greet(name: String) { println(name) }
- greet(name: String) -> { println(name) }
Show answer

fun greet(name: String) { println(name) } — Kotlin functions start with fun; parameters use the name: Type form.
Match function part to role

fun

Starts the function definition
name: String

String-typed parameter
{ }

Function body
greet("Ava")

Function call

Next lesson: Return values

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