PHP Variable

A variable in PHP is used to store data that can be manipulated or retrieved later. PHP variables are flexible and easy to use, making them a key part of any PHP script.

What Is a Variable in PHP?

A variable is a symbolic name for a value.

In PHP, variables are dynamically typed, meaning they can store any data type (e.g., string, integer, array).

Rules for Declaring Variables

Variables in PHP always start with a $ symbol.

The variable name must:

Start with a letter or an underscore _.

Contain only letters, numbers, or underscores.

Variable names are case-sensitive ($name and $Name are different).

Declaring a Variable

Use the $ symbol followed by a name to declare a variable.

Assign a value using the assignment operator (=).

Example:

<?php
$greeting = "Hello, World!"; // String variable
$age = 25; // Integer variable
$is_logged_in = true; // Boolean variable

echo $greeting; // Outputs: Hello, World!
?>

Variable Data Types

PHP automatically detects the data type of a variable. Common data types include:

  1. String: Text (e.g., "Hello")
  2. Integer: Whole numbers (e.g., 42)
  3. Float: Decimal numbers (e.g., 3.14)
  4. Boolean: true or false
  5. Array: A collection of values
  6. Object: Instance of a class
  7. NULL: No value

Example:

<?php
$name = "Alice";      // String
$age = 30;            // Integer
$height = 5.7;        // Float
$is_student = false;  // Boolean
$courses = ["Math", "Science"]; // Array
?>

Variable Scope

The scope determines where a variable can be accessed. PHP has three types of variable scope:

Local Scope: Accessible only within a function.

Global Scope: Accessible everywhere, except inside functions (unless declared global).

Static Variables: Retain their value between function calls.

Example:

<?php
// Global scope
$name = "John";

function displayName() {
    // Access global variable inside a function
    global $name;
    echo $name;
}

displayName(); // Outputs: John
?>

Variable Variables

You can use the value of one variable as the name of another variable.

Example:

<?php
// Declare a variable
$name = "John Doe"; // String
$age = 25;          // Integer
$isStudent = true;  // Boolean

// Use the variables
echo "Name: " . $name . "\n";
echo "Age: " . $age . "\n";
echo "Is Student: " . ($isStudent ? "Yes" : "No");
?>

Special Variables in PHP

$_POST: Used to collect form data sent via HTTP POST.

$_GET: Used to collect form data sent via HTTP GET.

$_SERVER: Contains information about server and execution environment.

Example: Working with PHP Variables

<?php
// Declare variables
$first_name = "Alice";
$last_name = "Johnson";
$age = 28;

// Concatenate strings
$full_name = $first_name . " " . $last_name;

// Output the values
echo "Name: " . $full_name . "<br>";
echo "Age: " . $age . "<br>";

// Arithmetic operation
$next_year_age = $age + 1;
echo "Next year, you will be " . $next_year_age . " years old.";
?>

Best Practices for PHP Variables

Use Descriptive Names

Use Descriptive Names: Make your variable names meaningful.

$user_age = 25; // Clear and descriptive

Avoid Overwriting Variables: Use unique names to avoid confusion.

Use Proper Case: Use camelCase or snake_case consistently.