When expression as powerful switch in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of when expression with multiple conditions

What is the output of this Kotlin code using when expression?

Kotlin

val x = 7
val result = when (x) {
    in 1..5 -> "Small"
    in 6..10 -> "Medium"
    else -> "Large"
}
println(result)

A Small

B Large

C Medium

D Compilation error

💡 Hint

Check which range the value 7 belongs to.

The value 7 falls in the range 6..10, so the when expression returns "Medium".

❓ Predict Output

intermediate

When expression with type checking

What will be printed by this Kotlin code using when with type checks?

Kotlin

fun describe(obj: Any): String = when (obj) {
    is String -> "String of length ${obj.length}"
    is Int -> "Integer: $obj"
    else -> "Unknown"
}

println(describe("Hello"))

A Integer: Hello

B String of length 5

C Unknown

D Compilation error

💡 Hint

Look at the type of the argument passed to describe.

The argument is a String "Hello" with length 5, so the when expression returns "String of length 5".

🔧 Debug

advanced

Identify the error in when expression with missing else

What error will this Kotlin code produce?

Kotlin

val y = 3
val output = when (y) {
    1 -> "One"
    2 -> "Two"
    else -> "Unknown"
}
println(output)

A Compilation error: 'when' expression must be exhaustive

B Runtime exception: No matching branch found

C Prints null

D Prints "One"

💡 Hint

Check if all possible values of y are covered.

The when expression is not exhaustive and lacks an else branch, so Kotlin reports a compilation error.

❓ Predict Output

advanced

When expression with complex conditions

What is the output of this Kotlin code using when with complex conditions?

Kotlin

val num = 15
val category = when {
    num % 3 == 0 && num % 5 == 0 -> "FizzBuzz"
    num % 3 == 0 -> "Fizz"
    num % 5 == 0 -> "Buzz"
    else -> "None"
}
println(category)

A None

B Fizz

C Buzz

D FizzBuzz

💡 Hint

Check divisibility of 15 by 3 and 5.

15 is divisible by both 3 and 5, so the first condition matches and returns "FizzBuzz".

❓ Predict Output

expert

When expression with smart casting and variable assignment

What will be the output of this Kotlin code using when with smart casting and variable assignment?

Kotlin

fun process(input: Any) {
    val result = when (input) {
        is String -> input.length
        is Int -> input * 2
        else -> -1
    }
    println(result)
}

process("Kotlin")

A 6

B 12

C Compilation error

D -1

💡 Hint

What is the length of the string "Kotlin"?

The input is a String "Kotlin" with length 6, so the when expression returns 6.