Comments and documentation markup in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Swift documentation comment usage

What will be the output when this Swift code is run?

Swift

/// Returns the sum of two integers.
/// - Parameters:
///   - a: The first integer
///   - b: The second integer
/// - Returns: The sum of a and b
func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}

print(add(3, 4))

A Compilation error due to comments

B Returns the sum of two integers.

C 3 4

D 7

💡 Hint

Documentation comments do not affect runtime output.

The triple slash comments (///) are used for documentation and do not affect the program execution. The function adds two numbers and prints the result.

❓ Predict Output

intermediate

Effect of nested multiline comments in Swift

What will be the output of this Swift code snippet?

Swift

/* Outer comment start
/* Inner comment */
Outer comment end */
print("Hello")

A Hello

B Compilation error due to nested comments

C /* Inner comment */ Hello

D No output, program crashes

💡 Hint

Swift supports nested multiline comments.

Swift allows nested multiline comments, so the entire comment block is ignored and the print statement runs normally.

❓ Predict Output

advanced

Output of code with single-line and multiline comments

What is printed when this Swift code runs?

Swift

// This is a single-line comment
let x = 5 /* This is a
multiline comment */
print(x)

A Compilation error due to comment placement

B 5

C

let x = 5
5

D 0

💡 Hint

Comments do not affect variable values.

Comments are ignored by the compiler. The variable x is assigned 5 and printed.

🧠 Conceptual

advanced

Purpose of documentation markup in Swift

Which option best describes the purpose of documentation markup comments (///) in Swift?

A They are used to disable code execution temporarily.

B They cause the compiler to optimize the code better.

C They generate documentation and help tools show info about code elements.

D They convert comments into runtime print statements.

💡 Hint

Think about how IDEs show help for functions.

Documentation comments provide structured info that tools use to generate docs and show quick help, but do not affect code execution.

🔧 Debug

expert

Identify the error caused by comment misuse

What error will this Swift code produce?

Swift

/* Start comment
// Single line comment inside
print("Hello")
/* Nested comment start
print("World")
*/
End comment */

A No error, prints nothing

B Prints Hello and World

C Syntax error: unterminated comment

D Prints Hello only

💡 Hint

Check if all multiline comments are properly closed.

Swift allows nesting of multiline comments. The outer comment properly closes at the final */. The entire code is commented out, so it compiles with no error and produces no output.

Practice

1. What is the main purpose of comments in Swift code?

easy

A. To create new variables

B. To make the code run faster

C. To explain the code for better understanding

D. To store user data

Solution

1. Step 1: Understand what comments do

   Comments are notes in the code that do not affect how the program runs but help explain what the code does.

2. Step 2: Identify the purpose of comments

   Comments make the code easier to read and understand for yourself and others who read the code later.

3. Final Answer:

   To explain the code for better understanding -> Option C

4. Quick Check:

   Comments explain code [OK]

Hint: Comments explain code, not run it or store data [OK]

Common Mistakes:

• Thinking comments speed up code
• Confusing comments with variables
• Using comments to store data

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

easy

A. # This is a comment

B. /* This is a comment */

C.

D. // This is a comment

Solution

1. Step 1: Recall Swift comment syntax

   Swift uses // for single-line comments and /* */ for multi-line comments.

2. Step 2: Match the correct syntax

   // This is a comment uses // which is the correct single-line comment syntax in Swift.

3. Final Answer:

   // This is a comment -> Option D

4. Quick Check:

   Single-line comment = // [OK]

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

Common Mistakes:

• Using /* */ for single-line comments
• Using HTML style comments
• Using # which is not a comment in Swift

3. What will the following Swift code output?

/// Adds two numbers
func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}
print(add(3, 4))

medium

A. 7

B. add(3, 4)

C. /// Adds two numbers

D. Error: Unexpected documentation comment

Solution

1. Step 1: Understand documentation comments effect

   The line starting with /// is a documentation comment and does not affect the code execution.

2. Step 2: Execute the function call

   The function add returns the sum of 3 and 4, which is 7, and print outputs it.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   Documentation comment ignored, output = 7 [OK]

Hint: Documentation comments don't change output, only explain [OK]

Common Mistakes:

• Thinking documentation comments print text
• Expecting error from documentation comments
• Confusing comments with code

4. Identify the error in this Swift code snippet:

/* This is a multi-line comment
func greet() {
    print("Hello")
}
// Missing closing comment delimiter

medium

A. Using // inside multi-line comment is invalid

B. Missing closing */ for multi-line comment

C. Function greet() is not declared properly

D. print statement syntax error

Solution

1. Step 1: Check multi-line comment syntax

   Multi-line comments start with /* and must end with */ to close properly.

2. Step 2: Identify missing closing delimiter

   The code has /* but no closing */, so the comment never ends, causing a syntax error.

3. Final Answer:

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

4. Quick Check:

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

Hint: Multi-line comments need /* and */ to open and close [OK]

Common Mistakes:

• Ignoring missing closing comment delimiter
• Thinking // can't be inside multi-line comments
• Assuming function syntax is wrong

5. You want to document a Swift function so that Xcode shows its description and parameters clearly. Which comment style should you use?

func multiply(_ x: Int, _ y: Int) -> Int {
    return x * y
}

hard

A. /// Multiplies two numbers
/// - Parameters:
/// - x: The first number
/// - y: The second number
/// - Returns: The product of x and y

B. /* Multiplies two numbers */

C. // This function multiplies two numbers

D.

Solution

1. Step 1: Understand documentation comment usage

   Documentation comments in Swift use /// and special markup to describe functions and parameters for tools like Xcode.

2. Step 2: Identify the detailed documentation style

   /// Multiplies two numbers /// - Parameters: /// - x: The first number /// - y: The second number /// - Returns: The product of x and y uses /// with - Parameters and - Returns tags, which is the correct way to document for Xcode's quick help.

3. Final Answer:

   /// Multiplies two numbers /// - Parameters: /// - x: The first number /// - y: The second number /// - Returns: The product of x and y -> Option A

4. Quick Check:

   Use /// with parameter tags for documentation [OK]

Hint: Use /// with - Parameters and - Returns for Xcode docs [OK]

Common Mistakes:

• Using single-line or multi-line comments without markup
• Using HTML style comments
• Not including parameter descriptions