PHP Variables

In PHP, variables are used to store data, which can then be used and manipulated throughout your script. Here’s a detailed overview of how variables work in PHP:

Declaring Variables

A variable in PHP starts with the $ sign, followed by the name of the variable.
Variable names in PHP are case-sensitive.

php
<?php
        $message = "Hello, World!";
        $age = 25;
        $price = 19.99;
    ?>

Variable Naming Rules

A variable name must start with a letter or an underscore (_).
A variable name cannot start with a number.
A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _).
Variable names are case-sensitive ($age and $AGE are two different variables).

php
<?php
        $name = "Alice";
        $Name = "Bob";
    
        echo $name; // Outputs: Alice
        echo $Name; // Outputs: Bob
    ?>

Variable Types

PHP is a loosely typed language, meaning you do not need to declare the data type of a variable. PHP automatically converts the variable to the correct data type, depending on its value.

Common Data Types:

String:

php
<?php
        $text = "Hello, World!";
    ?>

Integer:

php
<?php
        $number = 42;
    ?>

Float (Double):

php
<?php
        $price = 19.99;
    ?>

Boolean:

php
<?php
        $is_valid = true;
        $is_complete = false;
    ?>

Array:

php
<?php
        $colors = array("Red", "Green", "Blue");
    ?>

Object:

php
<?php
        class Car {
            public $color;
            public function __construct($color) {
                $this->color = $color;
            }
        }
    
        $myCar = new Car("Red");
    ?>

NULL:

php
<?php
        $empty = NULL;
    ?>

Variable Scope

Variables can be declared in different scopes, which determines their accessibility.

Global Scope:

Variables declared outside any function have a global scope and can be accessed outside functions.

php
<?php
        $x = 10;
    
        function myTest() {
            // Will generate an error because $x is not accessible inside the function
            echo $x;
        }
    
        myTest();
    ?>

Local Scope:

Variables declared within a function have a local scope and can only be accessed within that function.

php
<?php
        function myTest() {
            $y = 5; // Local scope
            echo $y;
        }
    
        myTest();
        // Will generate an error because $y is not accessible outside the function
        echo $y;
    ?>

Global Keyword:

Use the global keyword to access a global variable inside a function.

php
<?php
        $x = 10;
        $y = 20;
    
        function myTest() {
            global $x, $y;
            $y = $x + $y;
        }
    
        myTest();
        echo $y; // Outputs 30
    ?>

Static Variables:

Static variables retain their value between function calls.

php
<?php
        function myTest() {
            static $count = 0;
            echo $count;
            $count++;
        }
    
        myTest(); // Outputs 0
        myTest(); // Outputs 1
        myTest(); // Outputs 2
    ?>

Superglobals

PHP provides several built-in superglobal arrays that are always accessible, regardless of scope. These include:

$_GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION

Example using $_POST:

php
<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
        Name: <input type="text" name="name">
        <input type="submit">
    </form>
    
    <?php
        if ($_SERVER["REQUEST_METHOD"] == "POST") {
            $name = $_POST['name'];
            echo $name;
        }
    ?>

By understanding how to use variables effectively in PHP, you can store and manipulate data in your applications efficiently.

techmore.in