PHP: Constants, Comments, Operators

1. PHP Constants

A constant is an identifier whose value cannot be changed once defined.

Features of Constants: • Do not use $ symbol • Case-sensitive by default • Global scope

Defining Constants:

        define("SITE_NAME", "MyWebsite");
        echo SITE_NAME;

Using const keyword:

        const PI = 3.14;

2. PHP Comments

Comments are used to explain code and are ignored by the PHP interpreter.

Types of Comments:

1. Single-line comment

        // This is a single-line comment
        # This is also a single-line comment

1. Multi-line comment

        /*
         This is
         a multi-line comment
        */

3. PHP Operators

Operators are symbols used to perform operations on variables and values.

3.1 Arithmetic Operators

        echo 10 + 5;

3.2 Assignment Operators

3.3 Comparison Operators

        if ($a == $b) { }

3.4 Logical Operators

3.5 Increment / Decrement Operators

        $x++;
        $y--;

4. PHP Expressions

An expression is a combination of variables, operators, and values that produces a result.

Example:

        $result = ($a + $b) * 2;

5. PHP Regular Expressions

Regular Expressions (Regex) are used for pattern matching in strings.

Common PHP Regex Functions:

Example: Email Validation

        $email = "test@gmail.com";
        if (preg_match("/^[a-z0-9._%+-]+@[a-z0-9.-]+.[a-z]{2,}$/i", $email)) {
          echo "Valid Email";
        } else {
          echo "Invalid Email";
        }

Common Regex Patterns:

6. Advantages of PHP

Why Use PHP? • Open source and free • Easy to learn and use • Platform independent • Fast execution • Supports many databases • Large community support • Widely used in web development