Type conversion is always explicit in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code with explicit type conversion?

Consider the following Kotlin code snippet:

val x: Int = 10
val y: Long = x.toLong()
println(y + 5L)

What will be printed?

Kotlin

val x: Int = 10
val y: Long = x.toLong()
println(y + 5L)

A 15

B 15L

C 15.0

D Compilation error

💡 Hint

Remember that toLong() converts Int to Long explicitly.

The variable x is converted explicitly to Long using toLong(). Adding 5L (a Long) results in a Long value of 15. The println prints 15.

❓ Predict Output

intermediate

What error does this Kotlin code produce?

Look at this Kotlin code:

val a: Int = 100
val b: Long = a
println(b)

What error will it produce?

Kotlin

val a: Int = 100
val b: Long = a
println(b)

A Type mismatch: inferred type is Int but Long was expected

B No error, prints 100

C NullPointerException

D Unresolved reference: Long

💡 Hint

Kotlin requires explicit conversion between numeric types.

Kotlin does not allow implicit widening conversions. Assigning an Int to a Long variable without explicit conversion causes a type mismatch error.

🔧 Debug

advanced

Why does this Kotlin code fail to compile?

Examine this Kotlin snippet:

val num: Double = 12.5
val intNum: Int = num
println(intNum)

Why does it fail to compile?

Kotlin

val num: Double = 12.5
val intNum: Int = num
println(intNum)

A Because Double cannot be assigned to Int due to null safety

B Because println cannot print Int variables

C Because Kotlin requires explicit conversion from Double to Int using toInt()

D Because val variables cannot be reassigned

💡 Hint

Think about how Kotlin handles conversions between floating point and integer types.

Kotlin does not allow implicit conversion from Double to Int. You must use toInt() explicitly to convert.

❓ Predict Output

advanced

What is the output of this Kotlin code with explicit conversion and arithmetic?

Consider this Kotlin code:

val x: Byte = 10
val y: Int = x + 5
println(y)

What will be printed?

Kotlin

val x: Byte = 10
val y: Int = x + 5
println(y)

A Byte overflow error

B Compilation error due to type mismatch

C 10

D 15

💡 Hint

Check how Kotlin handles arithmetic with smaller integer types.

In Kotlin, arithmetic operations on Byte promote the value to Int. So x + 5 is an Int and can be assigned to y. The output is 15.

🧠 Conceptual

expert

Which Kotlin statement correctly converts a nullable Int to a non-nullable Long safely?

You have a nullable Int? variable num. You want to convert it to a non-nullable Long safely, providing 0L if num is null.

Which option does this correctly?

A val result: Long = num?.toLong() ?: 0L

B val result: Long = num.toLong()

C val result: Long = num ?: 0L

D val result: Long = num as Long

💡 Hint

Consider safe calls and the Elvis operator for null handling.

Option A uses the safe call ?. to convert num to Long only if it is not null, otherwise returns null. The Elvis operator ?: provides 0L if num is null. This safely converts nullable Int? to non-nullable Long.

Option A fails if num is null (throws exception). Option A tries to assign Int? or Long directly, which is invalid. Option A is an unsafe cast and will fail at runtime if num is not a Long.