Why expressions over statements matters in Kotlin - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

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

Consider this Kotlin code that uses expressions instead of statements. What will it print?

Kotlin

val result = if (5 > 3) "Yes" else "No"
println(result)

A 5

B No

C true

D Yes

💡 Hint

Remember, if in Kotlin can return a value.

The if expression returns "Yes" because 5 is greater than 3, so result is assigned "Yes" and printed.

🧠 Conceptual

intermediate

Why prefer expressions over statements in Kotlin?

Which of the following is the best reason to prefer expressions over statements in Kotlin?

A Expressions allow assigning results directly to variables, making code concise and clear.

B Expressions cannot be used inside functions.

C Statements run faster than expressions in Kotlin.

D Statements are required for all control flow in Kotlin.

💡 Hint

Think about how expressions can produce values.

Expressions produce values that can be assigned or used immediately, which helps write concise and readable code.

🔧 Debug

advanced

What error occurs in this Kotlin code mixing statements and expressions?

Look at this Kotlin code snippet. What error will it cause?

Kotlin

val x: String = if (true) println("Hello") else println("Bye")
println(x)

A No error, prints Hello and then Hello

B Type mismatch: inferred type is Unit but String was expected

C NullPointerException at runtime

D Syntax error: missing else branch

💡 Hint

Consider what println returns and what if expression expects.

println returns Unit, so the if expression returns Unit. Assigning it to val x expecting a String causes a type mismatch.

📝 Syntax

advanced

Which Kotlin code correctly uses expression style for conditional assignment?

Choose the Kotlin code snippet that correctly uses expressions to assign a value based on a condition.

A

val message
if (score > 50) message = "Pass" else message = "Fail"

B val message = if score > 50 { "Pass" } else { "Fail" }

C val message = if (score > 50) "Pass" else "Fail"

D val message = if (score > 50) { "Pass" } else

💡 Hint

Remember the syntax for if expressions in Kotlin.

Option C correctly uses if as an expression with parentheses and both branches returning values.

🚀 Application

expert

How many items are in the resulting list after using expression style map?

What is the size of the list result after running this Kotlin code?

Kotlin

val numbers = listOf(1, 2, 3, 4)
val result = numbers.map { if (it % 2 == 0) it * 2 else it }
println(result.size)

A 4

B 2

C 0

D Throws an exception

💡 Hint

Think about how map transforms each item but keeps the list size.

The map function returns a list with the same number of elements as the original list, here 4.