Web Technologies Tutorial

Introduction to PHP Functions

Functions are blocks of reusable code that perform specific tasks. They help in organizing code, improving readability, and reducing repetition. PHP comes with a large number of built-in functions and also allows you to create your own custom functions.

Defining Functions

In PHP, you can define a function using the function keyword, followed by the function name and a pair of parentheses.


<?php
function greet() {
    echo "Hello, World!";
}

// Calling the function
greet(); // Outputs: Hello, World!
?>

Functions with Parameters

Functions can accept parameters, which are variables passed to the function.


<?php
function greetPerson($name) {
    echo "Hello, $name!";
}

greetPerson("Alice"); // Outputs: Hello, Alice!
?>

Default Parameter Values

You can assign default values to function parameters.


<?php
function greetWithTitle($name, $title = "Mr./Ms.") {
    echo "Hello, $title $name!";
}

greetWithTitle("Bob"); // Outputs: Hello, Mr./Ms. Bob!
greetWithTitle("Alice", "Dr."); // Outputs: Hello, Dr. Alice!
?>

Returning Values

Functions can return values using the return statement.


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

$result = add(5, 3);
echo $result; // Outputs: 8
?>

Variable Scope

Variables defined inside a function have a local scope and can't be accessed outside the function.


<?php
function test() {
    $local_var = "I'm local";
    echo $local_var;
}

test(); // Outputs: I'm local
// echo $local_var; // This would cause an error
?>

Global Keyword

The global keyword allows you to access global variables from within a function.


<?php
$x = 5;

function useGlobal() {
    global $x;
    echo $x;
}

useGlobal(); // Outputs: 5
?>

Anonymous Functions

PHP supports anonymous functions, also known as closures.


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

$greet("Charlie"); // Outputs: Hello, Charlie!
?>

Arrow Functions (PHP 7.4+)

Arrow functions provide a more concise syntax for simple functions.


<?php
$multiply = fn($a, $b) => $a * $b;

echo $multiply(4, 5); // Outputs: 20
?>

Type Declarations

PHP 7+ allows you to specify the expected data types for function parameters and return values.


<?php
function addIntegers(int $a, int $b): int {
    return $a + $b;
}

echo addIntegers(5, 10); // Outputs: 15
// addIntegers("5", "10"); // This would trigger a TypeError
?>

Variadic Functions

Variadic functions can accept a variable number of arguments.


<?php
function sum(...$numbers) {
    return array_sum($numbers);
}

echo sum(1, 2, 3, 4); // Outputs: 10
?>

Recursive Functions

A recursive function is a function that calls itself.


<?php
function factorial($n) {
    if ($n <= 1) {
        return 1;
    }
    return $n * factorial($n - 1);
}

echo factorial(5); // Outputs: 120
?>

Best Practices

Use descriptive function names that indicate what the function does.
Keep functions small and focused on a single task.
Use type declarations to improve code reliability.
Document your functions with PHPDoc comments.
Avoid using global variables inside functions when possible.
Return values instead of printing them directly, to improve function reusability.

Conclusion

Functions are a fundamental building block of PHP programming. They allow you to create modular, reusable, and organized code. By mastering functions, you can write more efficient, maintainable, and scalable PHP applications. As you progress in your PHP journey, you'll find functions to be an indispensable tool in your programming toolkit.

PHP: Functions