Conditionals: if and else

A conditional runs code only when a condition is true.

Real-world analogy: "If it's raining, take an umbrella; otherwise, wear sunglasses."

Syntax

if (condition) {
    // runs when condition is true
} else if (otherCondition) {
    // runs when the first was false and this one is true
} else {
    // runs when none of the above were true
}

Example

fun main() {
    val temperature = 18

    if (temperature > 25) {
        println("It's hot")
    } else if (temperature > 15) {
        println("It's pleasant")
    } else {
        println("It's cold")
    }
}

Expected output

It's pleasant

Kotlin checks the conditions top to bottom and runs only the first branch that matches.

if is an expression

if produces a value, so it replaces the ternary operator found in other languages:

fun main() {
    val age = 20
    val status = if (age >= 18) "adult" else "minor"
    println(status)

    val a = 7
    val b = 12
    val larger = if (a > b) a else b
    println(larger)
}

adult
12

When if is used as an expression, the else branch is required — the expression must always produce a value.

Common mistakes

• Forgetting the parentheses: if age > 18 doesn't compile. Write if (age > 18).
• Putting conditions in the wrong order. if (score > 50) before if (score > 90) means the second can never run.

Practice

Store an age and print adult for 18 and over, teen for 13–17, and child otherwise.

fun main() {
    val age = 15

    if (age >= 18) {
        println("adult")
    } else if (age >= 13) {
        println("teen")
    } else {
        println("child")
    }
}

teen