Menu

Declaring Variables in PHP

Introduction

Declaring Variables in PHP

In PHP, variables are like containers that hold information or data. You can give them short names like $x, $y, or more meaningful names like $age, $carName, or $total_volume. Understanding how to declare and use variables properly is essential for writing effective PHP programs.

Rules for Declaring Variables in PHP

  • A variable starts with the $ sign, followed by the variable name.

  • The variable name must start with a letter (A-Z, a-z) or an underscore _.

  • Variable names cannot start with a number.

  • Variable names can only contain letters, numbers, and underscores (A–Z, 0–9, _).

  • Variable names are case-sensitive — for example, $age and $AGE are different variables.

  • Use descriptive names to make your code easy to understand.

Example: Declaring Variables and Outputting Them

<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;

echo $txt;
echo "<br>";
echo $x;
echo "<br>";
echo $y;
?>

Output:

Hello world!
5
10.5

Outputting Variables in PHP

Example 1: Using Variables Inside Strings

<?php
$txt = "cmrtpoint.com";
echo "I love $txt!";
?>

Output:
I love cmrtpoint.com!

Example 2: Concatenating Strings and Variables

<?php
$txt = "cmrtpoint.com";
echo "I love " . $txt . "!";
?>

Output:
I love cmrtpoint.com!

Example 3: Using Variables in Arithmetic Operations

<?php
$x = 5;
$y = 4;
echo $x + $y;
?>

Output:
9

PHP Is a Loosely Typed Language

You don’t need to declare the data type of a variable in PHP. PHP automatically converts the variable to the correct data type depending on the value you assign. This is different from languages like C, C++, or Java, where you must declare the type explicitly.

Variable Scope in PHP

A variable’s scope is the part of the script where it can be accessed or used. PHP has three main variable scopes:

  • Local Scope – Variables declared inside a function, accessible only within that function.

  • Global Scope – Variables declared outside a function, accessible throughout the script (except inside functions unless explicitly declared global).

  • Static Scope – Variables that retain their value even after the function finishes executing.

Global and Local Variables

Example: Global Scope Variable

<?php
$x = 5; // global scope

function myTest() {
    echo "<p>Variable x inside function is: $x</p>";
}

myTest();
echo "<p>Variable x outside function is: $x</p>";
?>

Output:

Variable x inside function is:
Variable x outside function is: 5

Example: Local Scope Variable

<?php
function myTest() {
    $x = 5; // local scope
    echo "<p>Variable x inside function is: $x</p>";
}

myTest();
echo "<p>Variable x outside function is: $x</p>";
?>

Output:

Variable x inside function is: 5
Variable x outside function is:

Using the global Keyword

<?php
$x = 5;
$y = 10;

function myTest() {
    global $x, $y;
    $y = $x + $y;
}

myTest();
echo $y; // Outputs 15
?>

Using the $GLOBALS Array

<?php
$x = 5;
$y = 10;

function myTest() {
    $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}

myTest();
echo $y; // Outputs 15
?>

The static Keyword

<?php
function myTest() {
    static $x = 0;
    echo $x;
    $x++;
}

myTest();  // Outputs 0
echo "<br>";
myTest();  // Outputs 1
echo "<br>";
myTest();  // Outputs 2
?>

Conclusion

Declaring variables in PHP is simple but must follow naming rules. Understanding how variables work — especially their scope (local, global, static) — helps you write cleaner and more efficient code. PHP’s flexibility with data types and variable scope makes it beginner-friendly and powerful.