TopolearnKotlin's expression-oriented control flow replaces the ternary operator and switch with something more powerful.
In Kotlin, if is an expression: it returns a value, so there is no ternary operator.
val max = if (a > b) a else bwhen replaces switch and is also an expression:
val label = when (code) {
200, 204 -> "ok"
in 400..499 -> "client error"
else -> "other"
}Branches can match constants, several values, ranges (in), types (is String), or arbitrary conditions when when has no subject (when { x < 0 -> ... }). There is no fall-through. When used as an expression, when must be exhaustive, usually via else. Kotlin 2.2 adds guard conditions: is Shape.Circle if s.radius > 10 -> ....
Loops:
for (i in 1..5)(inclusive),for (i in 0 until n)or0..<n(exclusive),for (i in 10 downTo 0 step 2).for (item in list), andfor ((index, item) in list.withIndex()).for ((key, value) in map).whileanddo { } while ()work as in Java.
break and continue work as usual, and labels (outer@ for ... with break@outer) exit nested loops.
Many loops become simpler with collection functions (forEach, map, filter), covered later; use for when you need early exits or index-heavy logic.
Example
fun classify(code: Int): String = when (code) {
200, 204 -> "ok"
in 300..399 -> "redirect"
in 400..499 -> "client error"
else -> "other"
}
fun main() {
val a = 3; val b = 7
val max = if (a > b) a else b
println(max) // 7
println(classify(204) + ", " + classify(404)) // ok, client error
for (i in 1..3) print(i) // 123
println()
for (i in 10 downTo 0 step 5) print("$i ") // 10 5 0
println()
for ((i, c) in "abc".withIndex()) print("$i$c ") // 0a 1b 2c
println()
outer@ for (x in 1..3) {
for (y in 1..3) if (x * y == 4) { println("found $x*$y"); break@outer } // found 2*2
}
}Remember
- if and when are expressions that return values
- when matches values, ranges, types or conditions with no fall-through
- 1..n is inclusive; until and ..< are exclusive
- Labels like break@outer exit nested loops
Watch out for
- Forgetting else in a when expression over an Int, which makes it non-exhaustive and fails to compile.