Functions are one of the most important building blocks in PHP. They allow you to group blocks of code into reusable, organized, and modular units.
A well-structured PHP program relies heavily on functions to avoid repetition, improve readability, and simplify debugging.

A function definition tells PHP what the function does, what parameters it accepts, and what value it returns.

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What Is a Function?

A function in PHP is a block of code designed to perform a specific task.
You can define it once and call it multiple times anywhere in your program.

PHP has two types of functions:

• Built-in functions (like strlen(), date(), var_dump())
• User-defined functions (created by you)

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Syntax for Defining a Function

function functionName() {
    // Code to be executed
}

Rules:

• Function names are not case-sensitive
• Must start with a letter or underscore
• Cannot start with a number

Example:

function greet() {
    echo "Welcome to PHP!";
}

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Calling a Function

Once defined, you can call the function anywhere in your script:

greet(); // Outputs: Welcome to PHP!

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Functions with Parameters

Functions can accept arguments, making them flexible and dynamic.

Example with One Parameter

function greetUser($name) {
    echo "Hello, $name!";
}

greetUser("Sagar");

Example with Multiple Parameters

function add($a, $b) {
    return $a + $b;
}

echo add(10, 20); // 30

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Default Parameter Values

You can assign default values to function parameters:

function welcome($name = "Guest") {
    echo "Welcome, $name!";
}

welcome();         // Welcome, Guest!
welcome("Sagar");  // Welcome, Sagar!

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Returning Values

Functions can return values using the return statement.

function multiply($x, $y) {
    return $x * $y;
}

$result = multiply(5, 3);
echo $result; // 15

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Variable Scope Inside Functions

Variables declared inside a function have local scope.

function demo() {
    $x = 10;  
}
echo $x; // Error: undefined

To access global variables inside a function, you must use:

global keyword

$site = "Savanka";

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

showSite();

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Functions with Return Type (PHP 7+)

You can specify the type of value a function should return:

function subtract(int $a, int $b): int {
    return $a - $b;
}

echo subtract(10, 3); // 7

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Anonymous Functions (Closures)

PHP allows creating unnamed functions:

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

$greet("Sagar");

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Best Practices

• Use meaningful function names.
• Keep functions short and focused on a single task.
• Use parameters and return values instead of global variables.
• Use type declarations for cleaner, safer code.
• Reuse functions to avoid code duplication.

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External Reference:
🔗 https://www.php.net/manual/en/

View Other Articles About PHP:
🔗 http://savanka.com/category/learn/php/