Comments and documentation syntax in Kotlin - Step-by-Step Execution

Concept Flow - Comments and documentation syntax

Start of code

↓

Check line

↓

Is comment?

↓

Ignore

↓

Next line

↓

End

The program reads each line, ignores comments, attaches documentation to code, and executes code lines.

Execution Sample

Kotlin

/**
 * This function prints a greeting
 */
fun greet() {
  // This is a comment
  println("Hello")
}

This code shows a function with a single-line comment, a documentation comment, and a print statement.

Execution Table

Step	Line Content	Type Detected	Action	Output/Effect
1	/**	Doc comment start	Start doc comment block	Begin doc capture
2	* This function prints a greeting	Doc comment line	Add to doc comment	Doc content stored
3	*/	Doc comment end	End doc comment block	Attach doc to function greet
4	fun greet() {	Code	Execute function start	Function greet defined
5	// This is a comment	Single-line comment	Ignore line	No effect
6	println("Hello")	Code	Execute print statement	Prints: Hello
7	}	Code	Execute function end	Function greet ends
8		End of code	Stop execution	Program ends

💡 Reached end of code, no more lines to process

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
docComment	empty	started	attached to greet	attached to greet
output	empty	empty	empty	Hello printed

Key Moments - 3 Insights

Why does the single-line comment not produce any output?

Because as shown in step 5 of the execution_table, single-line comments are detected and ignored, so they do not affect program output.

How does the documentation comment attach to the function?

Steps 1 to 3 show the doc comment block being captured and then attached to the function greet before execution continues.

Does the documentation comment affect the printed output?

No, the documentation comment is for humans and tools; only the code lines like println produce output, as seen in step 6.

Visual Quiz - 3 Questions

Look at the execution_table at step 5. What happens to the single-line comment?

A It is ignored and has no effect

B It is executed as code

C It prints a message

D It attaches to the function

💡 Hint

Check the 'Action' and 'Output/Effect' columns at step 5 in execution_table

At which step does the documentation comment finish attaching to the function?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Look for 'End doc comment block' and 'Attach doc to function greet' in execution_table

If the println line was changed to println("Hi"), what would change in variable_tracker?

A docComment would change

B No change at all

C output would show 'Hi printed'

D Function greet would not be defined

💡 Hint

Check the 'output' variable row in variable_tracker and relate it to the print statement in execution_table step 6

Concept Snapshot

Kotlin comments:
// single-line comment ignored by compiler
/* multi-line comment ignored */
/** documentation comment attached to code
 * used by tools
 */
Comments do not affect program output but help explain code.

Full Transcript

This visual trace shows how Kotlin code lines are processed one by one. Lines starting with // are single-line comments and ignored. Documentation comments start with /** and end with */, and their content is attached to the next code element, like a function. Code lines like println execute and produce output. The variable tracker shows how the documentation comment is stored and attached, while output captures printed text. Key moments clarify why comments don't print and how documentation is linked. The quiz tests understanding of comment handling and effects on output.

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