Comments and documentation syntax in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of code with single-line and multi-line comments

What is the output of this Kotlin code snippet?

Kotlin

fun main() {
    // This is a single-line comment
    val x = 5
    /* This is a
       multi-line comment */
    val y = 10
    println(x + y) // prints sum
}

A 15

B 510

C Compilation error due to comments

D 5 + 10

💡 Hint

Remember that comments do not affect the code execution.

Comments are ignored by the compiler. The code adds x and y (5 + 10) and prints 15.

❓ Predict Output

intermediate

Output of Kotlin code with KDoc documentation comments

What will be printed when running this Kotlin code?

Kotlin

/**
 * Returns the sum of two integers.
 * @param a first integer
 * @param b second integer
 * @return sum of a and b
 */
fun sum(a: Int, b: Int): Int {
    return a + b
}

fun main() {
    println(sum(3, 4))
}

A Compilation error due to KDoc

B sum of a and b

C 3 4

D 7

💡 Hint

Documentation comments do not affect runtime output.

KDoc comments are for documentation only and do not affect the program output. The sum function returns 7.

❓ Predict Output

advanced

Effect of nested comments in Kotlin

What happens when you try to compile and run this Kotlin code?

Kotlin

fun main() {
    /* Start of comment
    /* Nested comment */
    End of comment */
    println("Hello")
}

A Compilation error due to nested comments

B Prints Hello

C Prints /* Nested comment */

D Runtime error

💡 Hint

Kotlin does not support nested block comments.

Kotlin block comments cannot be nested. The compiler will raise an error.

❓ Predict Output

advanced

Output of code with commented out code lines

What is the output of this Kotlin program?

Kotlin

fun main() {
    val a = 10
    // val b = 20
    val c = 30
    // println(a + b)
    println(a + c)
}

A Compilation error due to b being undefined

B 40

C 30

D 10

💡 Hint

Commented out code does not run or affect variables.

The variable b and the print statement using b are commented out, so only a + c (10 + 30) is printed.

🧠 Conceptual

expert

Identifying correct KDoc usage for function documentation

Which of the following KDoc comments correctly documents a Kotlin function that returns the maximum of two integers?

A

/*
 * Returns max of two integers
 * @param a first integer
 * @param b second integer
 * @return larger integer
 */

B

// Returns max of a and b
// a: first integer
// b: second integer
// returns larger integer

C

/**
 * Returns the maximum of two integers.
 * @param a first integer
 * @param b second integer
 * @return the larger integer
 */

D

/**
 * Returns max of two integers
 * @param a first integer
 * @param b second integer
 * @param c unused parameter
 * @return larger integer
 */

💡 Hint

KDoc uses /** ... */ with @param and @return tags.

Option C uses proper KDoc syntax with correct tags. Option C uses single-line comments, not KDoc. Option C uses block comments but not KDoc style. Option C has an incorrect @param tag for a non-existent parameter.

Practice

1. Which of the following is the correct way to write a single-line comment in Kotlin?

easy

A. /* This is a single-line comment */

B.

C. // This is a single-line comment

D. # This is a single-line comment

Solution

1. Step 1: Identify single-line comment syntax in Kotlin

   Kotlin uses // to start a single-line comment.

2. Step 2: Compare options

   // This is a single-line comment uses //, which is correct. /* This is a single-line comment */ is for multi-line comments. <!-- This is a single-line comment --> is HTML style. # This is a single-line comment is used in some scripting languages but not Kotlin.

3. Final Answer:

   // This is a single-line comment -> Option C

4. Quick Check:

   Single-line comment = // [OK]

Hint: Single-line comments start with // in Kotlin [OK]

Common Mistakes:

• Using /* */ for single-line comments
• Using # or which are not Kotlin comments
• Confusing multi-line and single-line comment syntax

2. Which of the following is the correct syntax for a multi-line comment in Kotlin?

easy

A. /* This is a multi-line comment */

B.

C. /** This is a multi-line comment */

D. // This is a multi-line comment

Solution

1. Step 1: Recall multi-line comment syntax in Kotlin

   Kotlin uses /* ... */ to write multi-line comments.

2. Step 2: Analyze options

   /* This is a multi-line comment */ correctly uses /* ... */. // This is a multi-line comment is single-line comment syntax. /** This is a multi-line comment */ is documentation comment syntax. <!-- This is a multi-line comment --> is HTML comment syntax.

3. Final Answer:

   /* This is a multi-line comment */ -> Option A

4. Quick Check:

   Multi-line comment = /* ... */ [OK]

Hint: Multi-line comments use /* and */ to start and end [OK]

Common Mistakes:

• Using // for multi-line comments
• Confusing documentation comments /** */ with regular multi-line comments
• Using HTML style comments

3. What will be the output of the following Kotlin code?

fun main() {
    // println("Hello")
    println("World")
}

medium

A. Hello
World

B. World

C. Hello

D. No output

Solution

1. Step 1: Understand comment effect on code execution

   The line // println("Hello") is a comment, so it does not run.

2. Step 2: Identify which println runs

   Only println("World") runs, so output is "World".

3. Final Answer:

   World -> Option B

4. Quick Check:

   Commented code does not run = World [OK]

Hint: Commented lines do not execute, only uncommented print runs [OK]

Common Mistakes:

• Thinking commented println runs
• Expecting both lines to print
• Confusing comment syntax and output

4. Identify the error in the following Kotlin code snippet:

fun main() {
    /* This is a comment
    println("Hello")
}

medium

A. No error, code runs fine

B. Incorrect single-line comment syntax

C. Missing quotation marks in println

D. Missing closing */ for multi-line comment

Solution

1. Step 1: Check multi-line comment syntax

   The comment starts with /* but does not have a closing */.

2. Step 2: Understand impact of missing closing comment

   Without closing */, the compiler treats the rest as comment, causing syntax error.

3. Final Answer:

   Missing closing */ for multi-line comment -> Option D

4. Quick Check:

   Multi-line comments must close with */ [OK]

Hint: Always close multi-line comments with */ [OK]

Common Mistakes:

• Forgetting to close multi-line comments
• Confusing single-line and multi-line comment syntax
• Assuming code inside unclosed comment runs

5. Which comment style should you use in Kotlin to write documentation that tools can extract to generate API docs?

hard

A. /** This is a documentation comment */

B. /* This is a documentation comment */

C. // This is a documentation comment

D.

Solution

1. Step 1: Identify documentation comment syntax in Kotlin

   Kotlin uses /** ... */ for documentation comments that tools can parse.

2. Step 2: Compare with other comment types

   // This is a documentation comment is single-line comment syntax. /* This is a documentation comment */ is regular multi-line comment syntax. <!-- This is a documentation comment --> is HTML comment syntax.

3. Final Answer:

   /** This is a documentation comment */ -> Option A

4. Quick Check:

   Documentation comments use /** ... */ [OK]

Hint: Use /** ... */ for documentation comments in Kotlin [OK]

Common Mistakes:

• Using // or /* */ for documentation comments
• Confusing documentation comments with regular comments
• Using HTML comment style by mistake