Comments in PHP - Mini Project: Build & Apply

Comments in PHP

📖 Scenario: You are writing a simple PHP script to display a greeting message. To make your code clear for others and yourself, you will add comments explaining each part.

🎯 Goal: Learn how to write single-line and multi-line comments in PHP to explain your code.

📋 What You'll Learn

Create a PHP variable with a greeting message

Add a single-line comment explaining the variable

Add a multi-line comment explaining the print statement

Print the greeting message

💡 Why This Matters

🌍 Real World

Comments are used by developers everywhere to explain what their code does, making it easier to maintain and update.

💼 Career

Writing clear comments is a key skill for programmers, helping teams collaborate and ensuring code quality in professional projects.

1

Create a greeting variable

Create a PHP variable called $greeting and set it to the string "Hello, world!".

PHP

<?php

// Create a variable called $greeting and set it to "Hello, world!"

Hint

Use $greeting = "Hello, world!"; to create the variable.

2

Add a single-line comment

Add a single-line comment above the $greeting variable that says // This is the greeting message.

PHP

<?php
// Add a single-line comment explaining the greeting variable
$greeting = "Hello, world!";

Hint

Start the comment with // followed by your text.

3

Add a multi-line comment

Add a multi-line comment below the variable that says:
/* Print the greeting message to the screen
using echo statement */

PHP

<?php
// This is the greeting message
$greeting = "Hello, world!";

// Add a multi-line comment explaining the print statement

Hint

Use /* to start and */ to end the multi-line comment.

4

Print the greeting message

Write a line of PHP code to print the $greeting variable using echo.

PHP

<?php
// This is the greeting message
$greeting = "Hello, world!";

/* Print the greeting message to the screen
using echo statement */

// Print the greeting message

Hint

Use echo $greeting; to display the message.

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