When with multiple conditions in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of when with multiple conditions combined by commas

What is the output of this Kotlin code snippet?

Kotlin

fun main() {
    val x = 3
    val result = when (x) {
        1, 2 -> "One or Two"
        3, 4 -> "Three or Four"
        else -> "Other"
    }
    println(result)
}

A Three or Four

B Compilation error

C One or Two

D Other

💡 Hint

Remember that commas separate multiple matching values in a when branch.

The variable x is 3, and the when expression checks if x matches any of the values in each branch. The branch 3, 4 -> "Three or Four" matches because x is 3, so it returns "Three or Four".

❓ Predict Output

intermediate

When with condition ranges and multiple conditions

What will this Kotlin program print?

Kotlin

fun main() {
    val score = 85
    val grade = when (score) {
        in 90..100 -> "A"
        in 80..89, 75 -> "B"
        else -> "C"
    }
    println(grade)
}

A Runtime exception

B B

C C

D A

💡 Hint

Check if the score matches any of the conditions including the single value 75.

The score is 85, which falls in the range 80..89, so the branch in 80..89, 75 -> "B" matches and returns "B".

🔧 Debug

advanced

Identify the error in when with multiple conditions

What error does this Kotlin code produce?

Kotlin

fun main() {
    val y = 5
    val output = when (y) {
        1, 2 -> "Low"
        3, 4 -> "Medium"
        else -> "High"
    }
    println(output)
}

A No error, prints "Medium"

B TypeError: Cannot compare Int with Int

C SyntaxError: Missing comma between 3 and 4

D RuntimeException: Unreachable code

💡 Hint

Look carefully at the syntax between 3 and 4 in the when expression.

The branch 3 4 -> "Medium" is missing a comma between 3 and 4, which causes a syntax error in Kotlin.

❓ Predict Output

advanced

When with multiple conditions and else branch

What is the output of this Kotlin code?

Kotlin

fun main() {
    val input = "apple"
    val category = when (input) {
        "banana", "orange" -> "Citrus"
        "apple", "pear" -> "Pome"
        else -> "Unknown"
    }
    println(category)
}

A Pome

B Unknown

C Citrus

D Compilation error

💡 Hint

Check which branch matches the input string.

The input is "apple", which matches the branch "apple", "pear" -> "Pome", so the output is "Pome".

🧠 Conceptual

expert

How does Kotlin's when handle multiple conditions?

Which statement best describes how Kotlin's when expression handles multiple conditions separated by commas in a single branch?

A All conditions separated by commas must be true simultaneously for the branch to match.

B Multiple conditions separated by commas cause a compilation error.

C The branch matches only if the subject matches the first condition and ignores the rest.

D The branch matches if the subject equals any one of the listed conditions separated by commas.

💡 Hint

Think about how commas work in a when branch.

In Kotlin, when you separate multiple conditions by commas in a single branch, it means the branch matches if the subject equals any one of those conditions.

Practice

1.

What does the when expression do when multiple conditions are separated by commas in Kotlin?

easy

A. It throws an error if multiple conditions are used.

B. It checks if the value matches any of the listed conditions and executes the corresponding block.

C. It only checks the first condition and ignores the rest.

D. It requires all conditions to be true at the same time to execute the block.

Solution

1. Step 1: Understand how when handles multiple conditions

   In Kotlin, when multiple conditions are separated by commas, it means the when expression checks if the value matches any one of those conditions.

2. Step 2: Interpret the behavior of multiple conditions

   If the value matches any condition in the list, the corresponding block runs. It does not require all conditions to be true simultaneously.

3. Final Answer:

   It checks if the value matches any of the listed conditions and executes the corresponding block. -> Option B

4. Quick Check:

   Multiple conditions = any match triggers block [OK]

Hint: Multiple conditions mean OR logic, not AND [OK]

Common Mistakes:

• Thinking all conditions must be true at once
• Believing only the first condition is checked
• Assuming multiple conditions cause errors

2.

Which of the following is the correct syntax to check if a variable num is either 1, 2, or 3 using when with multiple conditions?

when (num) {
    ? -> println("Number is 1, 2, or 3")
    else -> println("Other number")
}

easy

A. 1, 2, 3

B. 1 || 2 || 3

C. 1 && 2 && 3

D. [1, 2, 3]

Solution

1. Step 1: Recall Kotlin when syntax for multiple conditions

   In Kotlin, multiple conditions in a when case are separated by commas without operators.

2. Step 2: Match the correct syntax

   1, 2, 3 uses commas to separate values: 1, 2, 3, which is correct. Other options use logical operators or list syntax, which are invalid here.

3. Final Answer:

   1, 2, 3 -> Option A

4. Quick Check:

   Multiple conditions use commas [OK]

Hint: Use commas, not operators, to separate conditions [OK]

Common Mistakes:

• Using || or && inside when conditions
• Trying to use list syntax like [1, 2, 3]
• Missing commas between values

3.

What will be the output of the following Kotlin code?

val x = 5
when (x) {
    1, 2, 3 -> println("Low")
    4, 5, 6 -> println("Medium")
    else -> println("High")
}

medium

A. Medium

B. High

C. Low

D. No output

Solution

1. Step 1: Identify the value of x

   The variable x is assigned the value 5.

2. Step 2: Match x with when conditions

   The second case checks if x is 4, 5, or 6. Since x is 5, this condition matches and prints "Medium".

3. Final Answer:

   Medium -> Option A

4. Quick Check:

   5 in 4,5,6 prints Medium [OK]

Hint: Check which group contains the value [OK]

Common Mistakes:

• Choosing the first matching group incorrectly
• Confusing else with matching values
• Assuming no output if multiple conditions exist

4.

Find the error in this Kotlin when expression:

val grade = 'B'
when (grade) {
    'A', 'B' -> println("Excellent")
    'C' || 'D' -> println("Good")
    else -> println("Try again")
}

medium

A. The variable grade should be an Int, not Char.

B. Using commas to separate 'A' and 'B' is wrong.

C. Missing parentheses around conditions.

D. Using '||' inside when conditions is invalid syntax.

Solution

1. Step 1: Review the when condition syntax

   In Kotlin, multiple conditions in a when case must be separated by commas, not logical operators like '||'.

2. Step 2: Identify the incorrect usage

   The line 'C' || 'D' uses '||', which is invalid syntax in when. It should be 'C', 'D'.

3. Final Answer:

   Using '||' inside when conditions is invalid syntax. -> Option D

4. Quick Check:

   Use commas, not logical operators [OK]

Hint: Never use || or && in when conditions [OK]

Common Mistakes:

• Using logical operators instead of commas
• Thinking commas are wrong separators
• Confusing variable types with syntax errors

5.

You want to write a Kotlin when expression that prints "Weekend" if the day is either "Saturday" or "Sunday", "Weekday" if the day is any other day of the week, and "Invalid" for any other input. Which code correctly implements this?

hard

A. when(day) {
in listOf("Saturday", "Sunday") -> println("Weekend")
else -> println("Weekday")
}

B. when(day) {
"Saturday" || "Sunday" -> println("Weekend")
else -> println("Weekday")
}

C. when(day) {
"Saturday", "Sunday" -> println("Weekend")
"Monday", "Tuesday", "Wednesday", "Thursday", "Friday" -> println("Weekday")
else -> println("Invalid")
}

D. when(day) {
"Saturday" && "Sunday" -> println("Weekend")
else -> println("Weekday")
}

Solution

1. Step 1: Check correct multiple condition syntax for weekend days

   when(day) { "Saturday", "Sunday" -> println("Weekend") "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" -> println("Weekday") else -> println("Invalid") } correctly uses commas to separate "Saturday" and "Sunday" to match either day.

2. Step 2: Verify handling of other days and else case

   when(day) { "Saturday", "Sunday" -> println("Weekend") "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" -> println("Weekday") else -> println("Invalid") } lists all weekdays explicitly and uses else for invalid inputs, matching the problem requirements.

3. Final Answer:

   when(day) { "Saturday", "Sunday" -> println("Weekend") "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" -> println("Weekday") else -> println("Invalid") } -> Option C

4. Quick Check:

   Use commas for multiple matches and else for fallback [OK]

Hint: List all matches with commas; use else for others [OK]

Common Mistakes:

• Using || or && instead of commas
• Missing else for invalid inputs
• Not listing all weekdays explicitly