PHP Comments

In PHP, comments are used to add notes or explanations to your code. They are ignored by the PHP engine and are not executed, which makes them useful for documenting your code, explaining logic, or temporarily disabling code during development.

PHP supports two types of comments:

1. Single-line Comments

Single-line comments are used to comment out a single line of code or a part of a line. They can be written in two ways:

a) Using double slashes (//):

• Everything after // on that line is treated as a comment.

// This is a single-line comment
$name = "John"; // This is an inline comment

Output:

• These comments do not produce any output when the script runs. They are purely for documentation purposes.

b) Using hash (#):

• This is another way to write single-line comments in PHP. It works the same way as //.

# This is also a single-line comment
$age = 30; # Inline comment

Both // and # are valid ways to write single-line comments, and you can choose whichever style you prefer.

2. Multi-line Comments

Multi-line comments allow you to comment out multiple lines of code. This is useful when you want to provide a detailed explanation or disable a block of code.

a) Using /* and */:

• Everything between /* and */ is considered a comment, even if it spans multiple lines.

/*
  This is a multi-line comment.
  You can use it to explain complex logic or comment out multiple lines of code.
*/
$city = "New York";  // This line is outside of the comment

You can also use multi-line comments to comment out code temporarily during development or debugging:

/*
$x = 10;
$y = 20;
$z = $x + $y;
*/

3. Doc Comments (PHPDoc)

PHP also supports a special type of comment called doc comments (or PHPDoc), which is used to generate documentation. These comments are typically placed above functions, classes, or methods to describe their purpose, parameters, return values, etc.

PHPDoc comments are enclosed by /** and */:

/**
 * This function adds two numbers.
 *
 * @param int $a The first number.
 * @param int $b The second number.
 * @return int The sum of $a and $b.
 */
function add($a, $b) {
    return $a + $b;
}

In this example:

• The @param tag describes the parameters of the function.
• The @return tag describes what the function will return.

This type of comment is especially useful when working with IDEs or generating documentation automatically.

When to Use Comments

1. Explaining Complex Code: If you have complicated code, comments can help you and others understand it later.

   // Multiply the result of two variables
   $result = $a * $b;
   

2. Documenting Functions and Classes: You can use PHPDoc to provide clear documentation about what each function or class does, including what parameters it expects and what it returns.

3. Disabling Code Temporarily: Comments are helpful when you want to temporarily disable a line or block of code.

   // echo "This will not be executed";  // Temporarily disabled
   

4. Providing Metadata: For larger projects, comments can be used to document important details, such as the date the code was written or any known issues with the code.

   // Created by John Doe on 2025-03-16
   // Note: The following code may need to be refactored later.
   

Conclusion

• Single-line comments: Use // or # for brief comments.
• Multi-line comments: Use /* ... */ for commenting out multiple lines.
• PHPDoc comments: Use /** ... */ for documentation purposes, especially for functions and classes.

Comments make your code more readable and maintainable, and they help others (or even your future self) understand your intentions and logic.