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

Challenge - 5 Problems

❓ Predict Output

intermediate

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

Consider the following Kotlin code snippet. What will be printed when it runs?

Kotlin

fun main() {
    val x = 10
    val result = if (x > 5) "Greater" else "Smaller or equal"
    println(result)
}

A true

B Smaller or equal

C Greater

D 10

💡 Hint

Remember that in Kotlin, if can return a value that you can assign to a variable.

The if expression checks if x is greater than 5. Since 10 is greater than 5, it returns "Greater" which is assigned to result and printed.

❓ Predict Output

intermediate

What value does the variable 'message' hold after this code runs?

Look at this Kotlin code. What is the value of 'message' after execution?

Kotlin

val number = 3
val message = if (number % 2 == 0) "Even" else "Odd"

A 3

B Odd

C Even

D true

💡 Hint

Check if the number is divisible by 2 without remainder.

3 % 2 equals 1, which is not zero, so the else branch "Odd" is assigned to message.

🧠 Conceptual

advanced

Which Kotlin code snippet correctly uses if as an expression to assign a value?

Select the option that correctly uses if as an expression returning a value in Kotlin.

A val result = if (a > b) a else b

B val result = if a > b { a } else { b }

C val result = if (a > b) { a } else

D val result = if (a > b) a; else b

💡 Hint

Remember the syntax for if expressions requires parentheses and else branch.

Option A correctly uses if as an expression with parentheses and else branch returning values. Other options have syntax errors.

❓ Predict Output

advanced

What is the output of this Kotlin code using nested if expressions?

Analyze the code and choose the output printed.

Kotlin

fun main() {
    val score = 75
    val grade = if (score >= 90) "A"
                else if (score >= 80) "B"
                else if (score >= 70) "C"
                else "F"
    println(grade)
}

A C

B B

C F

D A

💡 Hint

Check each condition from top to bottom to see which one matches first.

Score 75 is not >= 90 or 80 but is >= 70, so the grade is "C".

❓ Predict Output

expert

What is the output of this Kotlin code using if expression with side effects?

Consider this Kotlin code. What will be printed when it runs?

Kotlin

fun main() {
    var count = 0
    val result = if (++count > 0) {
        "Positive"
    } else {
        "Non-positive"
    }
    println("count = $count, result = $result")
}

A count = 0, result = Non-positive

B count = 0, result = Positive

C count = 1, result = Non-positive

D count = 1, result = Positive

💡 Hint

Remember that ++count increments before comparison.

++count increments count from 0 to 1 before comparison, so condition is true and result is "Positive".

Practice

1. What does it mean when if is used as an expression in Kotlin?

easy

A. It returns a value that can be assigned to a variable.

B. It can only be used without an else block.

C. It cannot be used inside functions.

D. It always causes a syntax error.

Solution

1. Step 1: Understand if as expression concept

   In Kotlin, if can return a value, unlike some other languages.

2. Step 2: Recognize usage in assignments

   This means you can assign the result of an if expression directly to a variable.

3. Final Answer:

   It returns a value that can be assigned to a variable. -> Option A

4. Quick Check:

   if returns value = D [OK]

Hint: Remember: Kotlin's if returns a value, assignable to variables [OK]

Common Mistakes:

• Thinking if cannot return values
• Forgetting to include else block
• Assuming if is only a statement

2. Which of the following is the correct syntax to assign the result of an if expression to a variable in Kotlin?

easy

A. val result if (x > 0) = "Positive" else "Non-positive"

B. val result = if (x > 0) "Positive" else "Non-positive"

C. val result = if (x > 0) { "Positive" }

D. val result = if x > 0 then "Positive" else "Non-positive"

Solution

1. Step 1: Check correct Kotlin if expression syntax

   The correct syntax uses if (condition) value1 else value2 inside an assignment.

2. Step 2: Identify errors in other options

   val result if (x > 0) = "Positive" else "Non-positive" has wrong order, C misses else, D uses invalid keywords.

3. Final Answer:

   val result = if (x > 0) "Positive" else "Non-positive" -> Option B

4. Quick Check:

   Correct syntax with else = A [OK]

Hint: Always include else and use parentheses in if expression [OK]

Common Mistakes:

• Omitting else block
• Wrong keyword order
• Missing parentheses around condition

3. What is the output of the following Kotlin code?

val x = 5
val result = if (x % 2 == 0) "Even" else "Odd"
println(result)

medium

A. Even

B. 5

C. Odd

D. SyntaxError

Solution

1. Step 1: Evaluate the condition x % 2 == 0

   Since 5 % 2 equals 1, the condition is false.

2. Step 2: Determine which branch executes

   Because the condition is false, the else branch returns "Odd".

3. Final Answer:

   Odd -> Option C

4. Quick Check:

   5 is odd = C [OK]

Hint: Check condition result carefully to pick correct branch [OK]

Common Mistakes:

• Assuming 5 is even
• Ignoring else branch
• Confusing modulo operation

4. Identify the error in this Kotlin code using if as an expression:

val x = 10
val result = if (x > 5) "Big"

medium

A. Incorrect variable declaration

B. Extra parentheses in if condition

C. Wrong comparison operator

D. Missing else branch for the if expression

Solution

1. Step 1: Check if expression completeness

   When using if as an expression, Kotlin requires an else branch to cover all cases.

2. Step 2: Identify missing else branch

   The code lacks an else branch, causing a compilation error.

3. Final Answer:

   Missing else branch for the if expression -> Option D

4. Quick Check:

   if expression needs else = B [OK]

Hint: Always add else when if returns a value [OK]

Common Mistakes:

• Omitting else block
• Assuming if can be incomplete
• Ignoring compiler errors

5. You want to write a Kotlin function that returns "Positive", "Negative", or "Zero" based on an integer input using if as an expression. Which code correctly implements this?

hard

A. fun checkNumber(n: Int): String = if (n > 0) "Positive" else if (n < 0) "Negative" else "Zero"

B. fun checkNumber(n: Int): String { if (n > 0) return "Positive" else if (n < 0) return "Negative" else return "Zero" }

C. fun checkNumber(n: Int): String = if (n > 0) "Positive" else "Negative"

D. fun checkNumber(n: Int): String = if n > 0 then "Positive" else if n < 0 then "Negative" else "Zero"

Solution

1. Step 1: Understand nested if as expression

   Kotlin allows nested if expressions to return values in a single expression.

2. Step 2: Check each option for correctness

   fun checkNumber(n: Int): String = if (n > 0) "Positive" else if (n < 0) "Negative" else "Zero" correctly uses nested if expressions with proper syntax and returns all cases. fun checkNumber(n: Int): String { if (n > 0) return "Positive" else if (n < 0) return "Negative" else return "Zero" } uses statements, not expression style. fun checkNumber(n: Int): String = if (n > 0) "Positive" else "Negative" misses the zero case. fun checkNumber(n: Int): String = if n > 0 then "Positive" else if n < 0 then "Negative" else "Zero" uses invalid syntax.

3. Final Answer:

   fun checkNumber(n: Int): String = if (n > 0) "Positive" else if (n < 0) "Negative" else "Zero" -> Option A

4. Quick Check:

   Nested if expression with else = A [OK]

Hint: Use nested if-else expressions for multiple return values [OK]

Common Mistakes:

• Missing else for zero case
• Using statement style instead of expression
• Incorrect syntax with then keyword