if and when

In Kotlin, if is an expression — it returns a value. You can assign that value, return it, or pass it directly:

val max = if (a > b) a else b

Multi-line bodies work too — the last expression of the chosen branch is the value:

val label = if (score >= 50) {
    println("nice work")
    "pass"
} else {
    "fail"
}

Implement larger(a, b) returning whichever is bigger. Write it in a single line: return if (a > b) a else b.

Starter code

fun larger(a: Int, b: Int): Int {
    return 0
}

when is the switch-on-steroids. It's also an expression — every branch produces a value:

val label = when (n) {
    1    -> "one"
    2, 3 -> "few"
    else -> "many"
}

Drop the subject to write boolean conditions in each branch — useful for ranges, guards, anything:

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

Implement letterGrade(score):

• 90 or above → "A"
• 80 to 89 → "B"
• 70 to 79 → "C"
• below 70 → "F"

Use when { ... } (no subject) with boolean conditions.

Starter code

fun letterGrade(score: Int): String {
    return ""
}

Both are conditional expressions. The choice is mostly readability:

// "if" is fine here:
val out = if (active) "on" else "off"

// "when" is much cleaner here:
val tier = when {
    score >= 90 -> "gold"
    score >= 70 -> "silver"
    score >= 50 -> "bronze"
    else        -> "none"
}

Anything you can write with chained if/else if you can usually rewrite with when — and when exhausts cleanly.

The classic. Implement fizzBuzz(n):

• divisible by both 3 and 5 → "FizzBuzz"
• divisible by 3 → "Fizz"
• divisible by 5 → "Buzz"
• otherwise → n.toString()

Use a subjectless when { ... } — each branch is condition -> value and the condition must be a Boolean. So write n % 3 == 0, not just n % 3 (which is an Int and the compiler will reject it).

Order matters: check divisibility by 15 first, otherwise a multiple of 15 will match the % 3 branch and never reach "FizzBuzz".

return when {
    n % 15 == 0 -> "FizzBuzz"
    // …fill in the rest
    else -> n.toString()
}

Starter code

fun fizzBuzz(n: Int): String {
    return when {
        // each branch is:  Boolean -> String
        // e.g.  n % 15 == 0 -> "FizzBuzz"
        else -> n.toString()
    }
}