When without argument in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of when without argument with conditions

What is the output of this Kotlin code using when without an argument?

Kotlin

fun main() {
    val x = 15
    val result = when {
        x % 3 == 0 -> "Divisible by 3"
        x % 5 == 0 -> "Divisible by 5"
        else -> "Not divisible by 3 or 5"
    }
    println(result)
}

A Compilation error

B Divisible by 3

C Not divisible by 3 or 5

D Divisible by 5

💡 Hint

Check which condition matches first in the when block.

The when block checks conditions in order. Since 15 is divisible by 3, the first condition is true, so it returns "Divisible by 3".

❓ Predict Output

intermediate

When without argument with Boolean expressions

What will this Kotlin program print?

Kotlin

fun main() {
    val a = 10
    val b = 20
    val output = when {
        a > b -> "a is greater"
        a == b -> "a equals b"
        else -> "a is smaller"
    }
    println(output)
}

A a is smaller

B a equals b

C a is greater

D Runtime exception

💡 Hint

Compare the values of a and b carefully.

Since 10 is less than 20, none of the first two conditions are true, so the else branch runs, printing "a is smaller".

🔧 Debug

advanced

Identify the error in when without argument

What error does this Kotlin code produce?

Kotlin

fun main() {
    val num = 5
    val result = when {
        num > 0 -> "Positive"
        num < 0 -> "Negative"
    }
    println(result)
}

A Prints "Negative"

B Runtime exception: NullPointerException

C Prints "Positive"

D Compilation error: 'when' must be exhaustive

💡 Hint

Check if all possible cases are covered in the when expression.

The when expression without an else branch is not exhaustive. Since num could be zero, the compiler requires an else branch or all cases covered.

🧠 Conceptual

advanced

Behavior of when without argument with multiple true conditions

In Kotlin, when using when without an argument, what happens if multiple conditions are true?

A Only the first true condition's branch executes

B All matching branches execute sequentially

C The last true condition's branch executes

D Compilation error due to ambiguity

💡 Hint

Think about how when expressions work as a control flow.

The when expression checks conditions in order and executes only the first branch whose condition is true.

🚀 Application

expert

Using when without argument to classify numbers

What is the output of this Kotlin program?

Kotlin

fun main() {
    val n = -7
    val classification = when {
        n > 0 && n % 2 == 0 -> "Positive even"
        n > 0 && n % 2 != 0 -> "Positive odd"
        n < 0 && n % 2 == 0 -> "Negative even"
        n < 0 && n % 2 != 0 -> "Negative odd"
        else -> "Zero"
    }
    println(classification)
}

A Negative even

B Positive even

C Negative odd

D Zero

💡 Hint

Check the sign and parity of n carefully.

n is -7, which is negative and odd, so the matching branch is "Negative odd".

Practice

1. What does when without argument do in Kotlin?

easy

A. It matches a value against constants only.

B. It checks boolean conditions one by one until one is true.

C. It creates a loop that runs multiple times.

D. It declares a variable with multiple types.

Solution

1. Step 1: Understand when without argument

   When used without an argument, when evaluates each condition as a boolean expression.

2. Step 2: Compare with other uses

   Unlike when with argument, it does not match values but checks conditions one by one.

3. Final Answer:

   It checks boolean conditions one by one until one is true. -> Option B

4. Quick Check:

   when without argument = boolean checks [OK]

Hint: Remember: no argument means boolean conditions checked [OK]

Common Mistakes:

• Thinking it matches values like switch-case
• Confusing it with loops
• Assuming it declares variables

2. Which of the following is the correct syntax for when without argument in Kotlin?

easy

A. when {
condition1 -> action1
condition2 -> action2
else -> defaultAction
}

B. when(value) {
1 -> action1
2 -> action2
else -> defaultAction
}

C. when (condition) {
true -> action1
false -> action2
}

D. when (value) {
condition1 -> action1
condition2 -> action2
}

Solution

1. Step 1: Identify when without argument syntax

   The correct syntax omits the argument and uses boolean conditions directly inside curly braces.

2. Step 2: Check options

   when { condition1 -> action1 condition2 -> action2 else -> defaultAction } matches this pattern with conditions and an else branch; others use an argument or incorrect structure.

3. Final Answer:

   when { condition1 -> action1 condition2 -> action2 else -> defaultAction } -> Option A

4. Quick Check:

   Correct syntax = when { condition1 -> action1 condition2 -> action2 else -> defaultAction } [OK]

Hint: No argument means conditions directly inside braces [OK]

Common Mistakes:

• Adding argument inside parentheses
• Missing else branch
• Using values instead of conditions

3. What is the output of this Kotlin code?

val x = 10
when {
  x < 5 -> println("Less than 5")
  x in 5..10 -> println("Between 5 and 10")
  else -> println("More than 10")
}

medium

A. More than 10

B. Less than 5

C. Between 5 and 10

D. No output

Solution

1. Step 1: Evaluate conditions in order

   First condition: x < 5 is false (10 < 5 is false). Second condition: x in 5..10 is true (10 is in 5 to 10).

2. Step 2: Execute matching branch

   Since second condition is true, it prints "Between 5 and 10" and stops checking further.

3. Final Answer:

   Between 5 and 10 -> Option C

4. Quick Check:

   10 in 5..10 = true [OK]

Hint: Check conditions top to bottom, first true runs [OK]

Common Mistakes:

• Assuming x < 5 is true
• Ignoring range check
• Expecting else branch output

4. Find the error in this Kotlin code using when without argument:

val y = 3
val result = when {
  y > 5 -> println("Greater than 5")
  y < 5 -> println("Less than 5")
}

medium

A. Missing else branch for unmatched cases

B. Incorrect use of parentheses after when

C. Conditions must be constants, not expressions

D. Cannot use println inside when

Solution

1. Step 1: Check when branches

   The code has two conditions but no else branch to handle all other cases.

2. Step 2: Understand Kotlin requirement

   When used without argument, Kotlin requires an else branch to cover all possibilities or the compiler errors about non-exhaustive when.

3. Final Answer:

   Missing else branch for unmatched cases -> Option A

4. Quick Check:

   Always add else branch [OK]

Hint: Always include else branch in when without argument [OK]

Common Mistakes:

• Ignoring else branch requirement
• Adding parentheses after when
• Thinking conditions must be constants

5. You want to print a message based on temperature:

val temp = 25
when {
  temp <= 0 -> println("Freezing")
  temp in 1..15 -> println("Cold")
  temp in 16..25 -> println("Warm")
  temp > 25 -> println("Hot")
  else -> println("Unknown")
}

What will be printed and why is this when usage correct?

hard

A. Compilation error due to overlapping ranges

B. "Cold"; because 25 is in 1..15 range

C. "Hot"; because 25 is greater than 25

D. "Warm"; because conditions cover all ranges with else as fallback

Solution

1. Step 1: Check which condition matches temp = 25

   temp <= 0 is false; temp in 1..15 is false; temp in 16..25 is true (25 is included).

2. Step 2: Confirm correctness of when usage

   All possible values are covered by conditions and else branch ensures fallback; no overlap causes error.

3. Final Answer:

   "Warm"; because conditions cover all ranges with else as fallback -> Option D

4. Quick Check:

   25 in 16..25 = true, else covers all [OK]

Hint: Check ranges carefully; else handles unexpected values [OK]

Common Mistakes:

• Misreading range boundaries
• Assuming 25 > 25 is true
• Thinking else is optional