Kotlin Conditions and Loops

if as an Expression

In Kotlin, if is an expression that returns a value — you can use it instead of a ternary operator:

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

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

when Expression

when is Kotlin's powerful replacement for switch:

val day = 3
val dayName = when (day) {
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    6, 7 -> "Weekend"
    else -> "Other"
}
println(dayName)  // Wednesday

// when without argument (acts like if-else chain)
when {
    score >= 90 -> println("Excellent!")
    score >= 60 -> println("Passed")
    else -> println("Failed")
}

for Loop with Ranges

for (i in 1..5) print("$i ")      // 1 2 3 4 5
for (i in 1 until 5) print("$i ") // 1 2 3 4
for (i in 5 downTo 1) print("$i ") // 5 4 3 2 1
for (i in 0..10 step 2) print("$i ") // 0 2 4 6 8 10

val fruits = listOf("apple", "banana", "cherry")
for (fruit in fruits) println(fruit)
for ((index, fruit) in fruits.withIndex()) {
    println("$index: $fruit")
}

while and do-while

var i = 0
while (i < 5) {
    print("$i ")
    i++
}

var x = 10
do {
    print("$x ")
    x -= 3
} while (x > 0)

break and continue with Labels

outer@ for (i in 1..3) {
    for (j in 1..3) {
        if (j == 2) continue@outer
        println("$i,$j")
    }
}