PHP Variables

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In PHP variables function as storage containers for data types like numbers, strings, arrays and objects. Programming with PHP variables lets you reuse existing data while modifying it throughout your application.

php-variables

Rules for Declaring PHP Variables

  • In PHP, any variable begins with a $ symbol which precedes the variable name.
  • The name of a PHP variable must start with a letter or the underscore character (_.
  • It cannot start with a number.
  • Variable names are case-sensitive ($name ≠ $Name).
  • PHP does not require you to specify variable data types because of its dynamic typing system.

Example

<?php
$name = "Alice";
$age = 25;
$price = 19.99;
$isAdmin = true;

echo "Name: $name, Age: $age, Price: $price, Admin: $isAdmin";
?>
Run ›

Variable Types

Type Example
String $name = "Alice";
Integer $age = 30;
Float $price = 45.99;
Boolean $isAdmin = true;
Array $fruits = ["apple", "banana"];
Object $user = new User();
NULL $value = null;

Variable Interpolation

Double-quoted strings allow you to directly embed PHP variables.

 

echo "Hello, $name"; // Works
echo 'Hello, $name'; // Doesn't interpolate

Variable Scope

Global Scope

A variable declared outside of a function remains inaccessible inside the function unless it is marked as global.

 

$siteName = "MySite";

function showSite() {
    global $siteName;
    echo $siteName;
}

Local Scope

A variable declared within a function remains accessible exclusively to that function.

 

function greet() {
    $message = "Hello!";
    echo $message;
}

Static Scope

Preserves variable value between function calls.

 

function counter() {
    static $count = 0;
    $count++;
    echo $count;
}

isset() and unset()

isset($name);  // Checks if variable is set
unset($name);  // Destroys the variable
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