Functions

A function is a way to name a chunk of code so you can reuse it. Instead of rewriting the same logic in multiple places, you write it once as a function and call it — which keeps your code clean. In Kotlin, you declare a function with the fun keyword.

kotlin

fun greet(name: String, day: String = "Sunday"): String {
    return "Hello $name, today is $day."
}

fun main() {
    println(greet("Aung"))
    println(greet("Hla", "Monday"))
}

You should see

Hello Aung, today is Sunday. Hello Hla, today is Monday.

Summary

Using functions improves code reuse, readability, and testing.

Easy traps

If you declare the return type as String but return a number, you'll get a type mismatch error.

Practical example — discount calculator

kotlin

fun calculateFinalPrice(price: Double, discountPercent: Double): Double {
    val discountAmount = price * discountPercent / 100
    return price - discountAmount
}

fun main() {
    val finalPrice = calculateFinalPrice(50000.0, 10.0)
    println("Final price: $finalPrice MMK")
}

You'll know it worked when: Final price: 45000.0 MMK