PHP Comments: Single-line Comments + Multi-line Comments

In PHP, comments are used to leave notes and explanations in the code, which are ignored by the PHP interpreter. They can be extremely helpful for both the developer who wrote the code and any other developers who might need to understand or modify the code later.

Here's a tutorial on how to use comments in PHP:

1. Single-Line Comments

Single-line comments are denoted by two forward slashes (//) or a hash symbol (#). The PHP interpreter will ignore everything on the line after these symbols.

Here's an example using //:

// This is a single-line comment
echo "Hello, World!";

And here's an example using #:

# This is also a single-line comment
echo "Hello, World!";

2. Multi-Line Comments

Multi-line comments are denoted by a forward slash followed by an asterisk (/*) at the beginning and an asterisk followed by a forward slash (*/) at the end. The PHP interpreter will ignore everything between these symbols, even if it spans multiple lines:

/*
This is a multi-line comment.
It can span as many lines as you like.
*/
echo "Hello, World!";

3. Inline Comments

Comments can also be used inline, meaning they can be placed on the same line as a piece of code:

echo "Hello, World!";  // This line prints "Hello, World!"

In this case, only the text after the // is considered a comment. The code before the // is executed normally.

4. Commenting Out Code

Finally, comments can be useful for temporarily disabling a piece of code:

// echo "This line won't be executed";
echo "This line will be executed";

In this case, the first line of code is commented out and won't be executed by the PHP interpreter. The second line will be executed normally.

Remember that good comments should describe why something is done in a certain way, not just what the code is doing. This makes it easier for others (or yourself in the future) to understand the reasoning behind the code.

How to Add Comments in PHP Code:
- Description: Basic single-line comment in PHP.
- Example Code:
```
// This is a single-line comment in PHP
```
PHP Multi-line Comment Example:
- Description: Use multi-line comments for longer explanations.
- Example Code:
```
/*
    This is a multi-line comment
    in PHP for extended explanations.
*/
```
Commenting Out Code Blocks in PHP:
- Description: Comment out entire blocks of code for testing or debugging.
- Example Code:
```
/*
    $variable = 42;
    echo "This line is commented out.";
*/
```
Removing or Commenting Lines of Code in PHP:
- Description: Commenting out lines for temporary exclusion.
- Example Code:
```
// $variable = 42; // Commented out for now
```

PHP Docblock Comments for Documenting Functions and Classes:

Description: Use docblock comments for documenting functions and classes.

Example Code:

/**
 * This is a docblock comment for a function.
 *
 * @param string $name The name parameter.
 * @return string The formatted greeting.
 */
function greet($name) {
    return "Hello, $name!";
}

PHP Comments vs. echo/print for Debugging:
- Description: Choose between comments and echo/print for debugging purposes.
- Example Code:
```
// Debugging with comments
// $variable = 42;

// Debugging with echo/print
// echo "Variable value: " . $variable;
```
Commenting Strategies for Collaborative PHP Development:
- Description: Adopt consistent commenting practices for collaborative development.
- Example Code:
```
// TODO: Implement feature X

// FIXME: Handle edge case Y
```

Commenting Conditional Statements in PHP:

Description: Add comments for clarity in conditional statements.

Example Code:

if ($condition) {
    // Code block executed when condition is true
} else {
    // Code block executed when condition is false
}

PHP Comments and Code Readability:
- Description: Use comments to enhance code readability.
- Example Code:
```
// Calculate the total price
$totalPrice = $quantity * $unitPrice;
```
PHP Comments for Code Explanations and Notes:
- Description: Provide explanations and notes using comments.
- Example Code:
```
// This loop iterates through the array
foreach ($items as $item) {
    // Process each item
}
```
Commenting HTML Within PHP Files:
- Description: Add comments for HTML content within PHP files.
- Example Code:
```
<?php
/*
    <div>
        This is an HTML comment within PHP.
    </div>
*/
?>
```
PHP Commenting Conventions and Standards:
- Description: Follow established conventions and standards for commenting.
- Example Code:
```
// Standard single-line comment
```