Functions in Kotlin are declared with fun:

fun greet(name: String): String {
    return "Hello, $name!"
}

// Single-expression function — the { return ... } can be shortened:
fun greetShort(name: String) = "Hello, $name!"

Default and named parameters

fun createUser(name: String, age: Int = 18, isAdmin: Boolean = false) {
    println("$name, age $age, admin=$isAdmin")
}

createUser("Ada")                          // age defaults to 18
createUser("Grace", age = 32)              // named argument
createUser(name = "Linus", isAdmin = true) // skip age entirely, using its default

Default parameters remove the need for multiple overloaded versions of the same function — a pattern you’ll see constantly in Android SDK code and in libraries like Retrofit later in this series.

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