Comments in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of PHP code with comments

What is the output of this PHP code snippet?

PHP

<?php
// This is a single-line comment
echo "Hello"; /* This is a
multi-line comment */
echo " World!";
?>

A

Hello
 World!

B Hello World!

C

Hello/* This is a
multi-line comment */ World!

D Syntax Error

💡 Hint

Remember that comments are ignored by PHP and do not affect output.

Single-line and multi-line comments are ignored by PHP. The echo statements print 'Hello' and ' World!' consecutively, resulting in 'Hello World!'.

🧠 Conceptual

intermediate

Purpose of comments in PHP

What is the main purpose of comments in PHP code?

A To explain the code to humans without affecting execution

B To make the code run faster

C To store data inside the code

D To create variables

💡 Hint

Think about what comments do when the PHP engine runs the code.

Comments are ignored by PHP when running the code. They help programmers understand the code by adding explanations or notes.

❓ Predict Output

advanced

Output with nested comment-like syntax

What will this PHP code output?

PHP

<?php
/* Start comment
// This is not a comment
echo "Hello";
End comment */
echo "World!";
?>

A Hello

B HelloWorld!

C World!

D Syntax Error

💡 Hint

Remember that everything inside /* */ is ignored, even if it looks like code.

The entire block between /* and */ is a comment, so echo "Hello"; is ignored. Only echo "World!"; runs, printing 'World!'.

📝 Syntax

advanced

Identify syntax error with comments

Which option will cause a syntax error in PHP?

A <?php /* Unclosed multi-line comment

B <?php // Comment without closing tag

C <?php echo "Hello"; // Proper comment

D

<?php # Single-line comment
 echo "Hi"; ?>

💡 Hint

Check if all multi-line comments are properly closed.

Option A has an unclosed multi-line comment which causes a syntax error. All other options have valid comments.

🚀 Application

expert

Count lines of code excluding comments

Given this PHP code, how many lines of actual code (not comments or blank lines) does it contain?

PHP

<?php
// Initialize
$a = 5;
/* Multi-line
comment here */
$b = 10;

# Another comment
$c = $a + $b;
echo $c;
?>

A 3

B 5

C 6

D 4

💡 Hint

Count only lines with actual PHP code, ignore comments and empty lines.

The code lines are: $a = 5;, $b = 10;, $c = $a + $b;, and echo $c;. Total 4 lines.

Practice

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

easy

A.

B. // This is a single-line comment

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

D. # This is not a comment

Solution

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

   PHP supports single-line comments using // and #.

2. Step 2: Check each option

   // This is a single-line comment uses // correctly. is HTML comment syntax, not PHP. /* This is a single-line comment */ is multi-line comment syntax. # This is a single-line comment is also valid in PHP, so # This is not a comment is correct as well.

3. Final Answer:

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

4. Quick Check:

   Single-line comment = // or # [OK]

Hint: Single-line comments start with // or # in PHP [OK]

Common Mistakes:

• Confusing HTML comments with PHP comments
• Using multi-line comment syntax for single-line comments
• Thinking # is not a valid comment

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

easy

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

B. // This is a multi-line comment

C. # This is a multi-line comment

D.

Solution

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

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

2. Step 2: Evaluate each option

   /* This is a multi-line comment */ correctly uses /* ... */. Options B and C are single-line comment styles. 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 /* at start and */ at end [OK]

Common Mistakes:

• Using // or # for multi-line comments
• Confusing HTML comments with PHP comments
• Forgetting to close multi-line comment with */

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

<?php
// echo 'Hello';
echo 'World';
?>

medium

A. HelloWorld

B. No output

C. Hello

D. World

Solution

1. Step 1: Understand the effect of the comment

   The line // echo 'Hello'; is commented out, so it does not run.

2. Step 2: Identify the executed code

   The line echo 'World'; runs and prints "World".

3. Final Answer:

   World -> Option D

4. Quick Check:

   Commented out code does not run, so output = World [OK]

Hint: Code after // is ignored, only uncommented code runs [OK]

Common Mistakes:

• Thinking commented code runs
• Confusing output by combining commented and uncommented lines
• Ignoring that echo prints text

4. Find the error in the following PHP code:

<?php
/* This is a comment
 echo 'Hello';
// Missing closing tag
?>

medium

A. PHP tags are incorrect

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

C. Missing closing */ for multi-line comment

D. echo statement syntax error

Solution

1. Step 1: Check multi-line comment syntax

   The multi-line comment starts with /* but never ends with */.

2. Step 2: Understand consequences of missing closing comment

   Without closing */, PHP treats the rest as comment, causing syntax errors or unexpected behavior.

3. Final Answer:

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

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
• Thinking // cannot be inside multi-line comments
• Misreading PHP tags as error

5. You want to temporarily disable a block of code without deleting it. Which comment style should you use in PHP to do this safely for multiple lines?

hard

A. Use /* at start and */ at end of the block

B. Use # at the start of the block

C. // Comment each line with //

D. Wrap the block with

Solution

1. Step 1: Understand commenting multiple lines

   Using /* ... */ allows commenting multiple lines at once safely.

2. Step 2: Evaluate other options

   // Comment each line with // requires adding // on each line, which is tedious. Use # at the start of the block is invalid for multiple lines. Wrap the block with is HTML comment syntax, not PHP.

3. Final Answer:

   Use /* at start and */ at end of the block -> Option A

4. Quick Check:

   Multi-line comments use /* ... */ [OK]

Hint: Use /* ... */ to comment multiple lines quickly [OK]

Common Mistakes:

• Using # or // for many lines without repeating
• Confusing HTML comments with PHP comments
• Not closing multi-line comments properly