Comments in PHP are lines of code that are not executed by the PHP interpreter. They are used to annotate the code, making it easier to understand and maintain. Comments can explain the purpose of code blocks, clarify complex logic, or temporarily disable parts of the code. PHP supports three types of comments:

1. Single-Line Comments

Single-line comments are used to comment out a single line of code. Anything following the comment marker on that line will be ignored by the PHP interpreter.

• Syntax:

  // This is a single-line comment using double slashes
  # This is another single-line comment using a hash symbol
  

• Example:

  <?php
  $greeting = "Hello, World!"; // This is a single-line comment explaining the greeting variable
  echo $greeting; // Output the greeting message
  
  # This is another way to write a single-line comment
  $number = 42; # Assigning the value 42 to the variable $number
  ?>
  

  In this example:

  • // and # are used to comment out individual lines. The code following these symbols on the same line will not be executed.

2. Multi-Line Comments

Multi-line comments are used to comment out multiple lines of code or provide more detailed explanations. This type of comment is useful when you need to explain a larger section of code.

• Syntax:

  /*
    This is a multi-line comment.
    It can span multiple lines.
  */
  

• Example:

  <?php
  /*
    The following block of code calculates the sum
    of two numbers and stores the result in the $sum variable.
  */
  $a = 10;
  $b = 20;
  $sum = $a + $b;
  
  echo $sum; // Outputs: 30
  ?>
  

  In this example:

  • The multi-line comment explains the purpose of the code block in detail. Everything between /* and */ is ignored by the PHP interpreter.

3. Using Comments to Temporarily Disable Code

Comments can also be used to temporarily disable a piece of code without deleting it. This is helpful during debugging or testing.

• Example:

  <?php
  $x = 5;
  $y = 10;
  
  // $sum = $x + $y; // This line is temporarily disabled
  
  echo "Sum is disabled temporarily.";
  ?>
  

  In this example:

  • The line $sum = $x + $y; is commented out using //, so it won’t be executed. You can easily uncomment it later by removing the //.

4. Best Practices for Using Comments

• Be Descriptive but Concise: Write comments that clearly explain the code without being overly verbose.

• Keep Comments Up-to-Date: Ensure that comments reflect the current state of the code. Outdated comments can be misleading.

• Use Comments for Clarification: Comments should clarify the "why" behind the code, especially in complex or non-obvious sections. They should not simply restate what the code does.

• Avoid Over-Commenting: Don’t comment every line of code. Use comments where they add value, not for trivial code that is self-explanatory.