PHP Basics Tutorial – Variable Scope in PHP

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Understand variable scope in PHP, including local and global variables. Learn how to use the global keyword and access global variables inside functions with clear code examples.

What is Variable Scope?

The scope of a variable refers to where it is accessible within the code.

Local Scope:

A variable defined inside a function is local to that function and cannot be accessed outside.

Example: Local Scope

<?php
function testFunction() {
    $x = 10;  // Local variable
    echo $x;  // Output: 10
}

testFunction();
echo $x;  // Error: Undefined variable
?>

Global Scope:

Variables defined outside functions are global and can be accessed globally.

<?php
$x = 10;  // Global variable

function testFunction() {
    echo $GLOBALS['x'];  // Accessing global variable
}

testFunction();  // Output: 10
?>

$GLOBALS - The $GLOBALS array is an associative array with the name of the global variable being the key and the contents of that variable being the value of the array element.

$GLOBALS exists in any scope, this is because $GLOBALS is a superglobal.

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

function myTest() {
    $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
} 
     
myTest();
echo $y; // outputs 15
?>

Global Keyword:

To use a global variable inside a function, use the global keyword.

<?php
$x = 10;  // Global variable

function testFunction() {
    global $x;
    echo $x;  // Output: 10
}

testFunction();
?>

Tasks

Task 1: Understanding Local Scope

Create a function called printLocalVar() that defines a local variable $message with the value "Hello, PHP!".
Print $message inside the function.
Call the function and observe the output.
Now, try to print $message outside the function. What happens? Explain why.

Example Structure:

<?php
function printLocalVar() {
    // Your code here
}
// Call function and test
?>

Task 2: Working with Global Scope

Define a global variable $counter = 0; outside any function.
Create a function incrementCounter() that accesses $counter using the $GLOBALS array and increments it by 1.
Call the function twice and then print $counter outside the function. What is the output?

Expected Output:

Task 3: Modifying Global Variables Inside a Function

Define a global variable $total = 50;.
Create a function applyDiscount() that:
- Uses the global keyword to access $total.
- Applies a 10% discount (reduce $total by 10%).
Call the function and then print $total outside the function.