When as expression returning value in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of when expression returning a value

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

Kotlin

val x = 3
val result = when (x) {
    1 -> "One"
    2 -> "Two"
    3 -> "Three"
    else -> "Unknown"
}
println(result)

A Three

B Two

C One

D Unknown

💡 Hint

Check which case matches the value of x.

The variable x is 3, so the when expression returns "Three".

❓ Predict Output

intermediate

When expression with multiple matching conditions

What will this Kotlin code print?

Kotlin

val y = 5
val output = when (y) {
    in 1..4 -> "Low"
    in 5..10 -> "Medium"
    else -> "High"
}
println(output)

A Low

B Syntax Error

C High

D Medium

💡 Hint

Look at the range that includes 5.

The value 5 falls in the range 5..10, so the when expression returns "Medium".

❓ Predict Output

advanced

When expression with smart casting and return value

What is the output of this Kotlin code?

Kotlin

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

println(describe("Hello"))

A Integer value Hello

B String of length 5

C Unknown type

D Compilation error

💡 Hint

Check the type of the argument passed to describe.

The argument is a String "Hello". The when expression smart casts it to String and returns its length.

❓ Predict Output

advanced

When expression with no matching branch and else clause

What will this Kotlin code print?

Kotlin

val z = 100
val result = when (z) {
    in 1..10 -> "Small"
    in 11..50 -> "Medium"
    else -> "Large"
}
println(result)

A Medium

B Small

C Large

D Runtime exception

💡 Hint

Check which condition matches the value 100.

100 does not fall in 1..10 or 11..50, so the else branch returns "Large".

❓ Predict Output

expert

When expression returning different types and type inference

What is the type and value of result after running this Kotlin code?

Kotlin

val input: Any = 42
val result = when (input) {
    is Int -> input * 2
    is String -> input.length
    else -> 0
}
println(result)

A Type: Int, Value: 84

B Type: String, Value: "42"

C Type: Any?, Value: null

D Type: Int, Value: 42

💡 Hint

Look at the type of input and what each branch returns.

The input is an Int 42, so the when expression returns 42 * 2 = 84. The inferred type is Int.