Kotlin — If Else

Basic if

fun main() {
    val temperature = 28

    if (temperature > 25) {
        println("It's warm!")
    }
}

if as expression

fun main() {
    val x = 10
    val label = if (x > 5) "big" else "small"
    println(label) // big
}

if-else if-else

fun main() {
    val score = 85

    val grade = if (score >= 90) "A"
    else if (score >= 80) "B"
    else if (score >= 70) "C"
    else "F"

    println(grade) // B
}

when expression

fun main() {
    val day = 3

    val name = when (day) {
        1 -> "Monday"
        2 -> "Tuesday"
        3 -> "Wednesday"
        4 -> "Thursday"
        5 -> "Friday"
        6, 7 -> "Weekend"
        else -> "Invalid"
    }

    println(name) // Wednesday
}

when with ranges

fun main() {
    val score = 85

    val grade = when (score) {
        in 90..100 -> "A"
        in 80..89 -> "B"
        in 70..79 -> "C"
        in 60..69 -> "D"
        else -> "F"
    }

    println(grade) // B
}

when with type checking

fun main() {
    val obj: Any = "hello"

    when (obj) {
        is Int -> println("Int: $obj")
        is String -> println("String: $obj")
        is List<*> -> println("List of size ${obj.size}")
        else -> println("Other")
    }
}

Nested conditions

fun main() {
    val age = 25
    val hasTicket = true

    if (age >= 18) {
        if (hasTicket) {
            println("Welcome!")
        } else {
            println("Need a ticket")
        }
    } else {
        println("Must be 18+")
    }
}

Mini Practice

Write Kotlin code that:

1. Uses if as an expression to assign a value
2. Uses when with ranges to classify a score
3. Uses when with type checking
4. Combines conditions with && and ||

Up Next

In the next lesson, you'll learn about Loops — for, while, and iteration in Kotlin.