What Are Comments in PHP?

Comments are pieces of text in your PHP code that the interpreter ignores. They serve as notes for developers to understand the code better.

Types of Comments in PHP

PHP supports three types of comments:

Single-line comments (// and #)

Multi-line comments (/* */)

DocBlock comments (/** */) for documentation.

Single-line Comments in PHP

Use // or # to create comments for a single line.

Example

<?php
// This is a single-line comment using double slashes.
echo "Hello, World!"; // This explains the line of code.

# This is another way to write a single-line comment.
echo "PHP is fun!";
?>

Multi-line Comments in PHP

Use /* */ for comments that span multiple lines.

Great for explaining large sections of code or temporarily disabling code blocks.

Example

<?php
/*
This is a multi-line comment.
It can span multiple lines.
Useful for detailed explanations.
*/
echo "Learning PHP multi-line comments!";
?>

DocBlock Comments in PHP

DocBlock comments are a special kind of multi-line comment used for documentation.

Use /** */ and include annotations like @param, @return, etc.

Typically used for functions, classes, and methods.

Example

<?php
/**
 * Calculate the sum of two numbers.
 *
 * @param int $a The first number.
 * @param int $b The second number.
 * @return int The sum of the numbers.
 */
function add($a, $b) {
    return $a + $b;
}
?>

Practical Uses of Comments in PHP

A. Explain Your Code:

Comments describe what your code does for better readability.

<?php
// Calculate the total price including tax
$price = 100;
$tax = 0.05; // 5% tax
$total = $price + ($price * $tax);
echo $total;
?>

B. Debugging:

Temporarily disable parts of code using comments to identify issues.

<?php
echo "This will run.";

// The line below won't run because it is commented out.
// echo "This is a disabled line.";

echo "Debugging with comments!";
?>

C. Provide Documentation:

Use DocBlocks to document functions, especially for team projects.

Tips for Writing Good Comments

Explain Why, Not What: Avoid redundant comments.

// Bad comment
$price = 100; // Assigning 100 to price variable

// Good comment
$price = 100; // Setting the base price of the product

Keep Comments Updated: Ensure comments match the code after edits.

Use DocBlocks for Complex Functions: These help other developers understand parameters, return values, and purpose.

Common Mistakes to Avoid

Over-commenting: Too many comments can clutter code.

Commenting Obvious Code: Avoid stating what’s apparent from the code itself

Interactive Example

<?php
// Step 1: Define variables
$price = 200; // Base price of the item
$discount = 20; // Discount in percentage

/* 
Step 2: Calculate final price
Discount is subtracted from the price
*/
$final_price = $price - ($price * $discount / 100);

/**
 * Display the final price
 * This block explains the output.
 */
echo "The final price is: " . $final_price;
?>

Why Are Comments Important?

Improve code readability.

Help with debugging and maintenance.

Assist in collaboration by documenting code.

Best Practices for Writing PHP Comments

Writing effective comments in PHP improves code readability, maintainability, and collaboration. Here’s how you can ensure your comments are meaningful and adhere to best practices:

Use Comments to Explain Why, Not What

Avoid stating what the code already makes clear.

Focus on explaining the purpose or reasoning behind complex logic.

Example:

<?php
// Good comment: Explains purpose
// This calculates the total price including tax
$total_price = $price + ($price * $tax_rate);

// Bad comment: Repeats the code
// Adds price and tax
$total_price = $price + ($price * $tax_rate);
?>

Use // for short, specific explanations.

Avoid long comments that disrupt code readability.

Example:

<?php
// Check if the user is logged in
if ($is_logged_in) {
    echo "Welcome back!";
}
?>

Use /* */ for explaining large sections or complex logic.

Clearly separate code blocks for readability.

Example:

<?php
/*
This function calculates the discount based on:
- Total purchase amount
- Membership status of the user
*/
function calculateDiscount($amount, $is_member) {
    return $is_member ? $amount * 0.1 : $amount * 0.05;
}
?>

Use /** */ to document functions or classes.

Include tags like @param and @return for clarity.

Example:

<?php
/**
 * Calculate the total price including tax.
 *
 * @param float $price The base price.
 * @param float $tax_rate The applicable tax rate.
 * @return float The total price after tax.
 */
function calculateTotalPrice($price, $tax_rate) {
    return $price + ($price * $tax_rate);
}
?>

Too many comments can clutter the code.

Only comment on complex logic or non-obvious aspects.

Example:

<?php
// Poor: Over-commenting
// Define a variable
$name = "John"; // Assign value "John" to variable

// Better: Comment only where needed
// Store the user's name for the session
$name = "John";
?>

When you change code, update related comments to avoid confusion.

Outdated comments can mislead developers.

Follow a consistent style for all comments.

For example:

Start with a capital letter.

End with a period for complete sentences.

Example:

<?php
// Check user authentication status.
if ($is_authenticated) {
    // Display welcome message.
    echo "Welcome, User!";
}
?>

Don’t include passwords, API keys, or sensitive data in comments.

Use TODO comments to highlight unfinished tasks or areas that need improvement.

Example:

<?php
// TODO: Implement user role validation
function checkUserRole($role) {
    // Placeholder for role checking logic
    return true;
}
?>

Temporarily disable parts of your code and leave comments to explain why.

Example:

<?php
// Temporarily disabled for debugging
// echo "Debugging this feature.";
?>