Learn

In Kotlin, if is an expression — it returns a value:

val label = if (n > 0) "positive" else if (n < 0) "negative" else "zero"

No ternary operator — if/else does the job.

when is Kotlin's pattern-match-y switch. Much more flexible than Java's switch:

val grade = when {
    score >= 90 -> "A"
    score >= 80 -> "B"
    score >= 70 -> "C"
    else -> "F"
}

val kind = when (x) {
    0, 1 -> "low"
    in 2..10 -> "medium"        // range
    is String -> "a string"     // type check
    else -> "other"
}

when can match values, ranges, types, or arbitrary boolean conditions. Like if, it's an expression.