PH PHP

PHP: Functions

What you will learn

How to define functions, use default parameters, type declarations, and variable scope.

Defining a function

function greet($name) {
    return "Hello, $name!";
}
echo greet("Alice");  // Hello, Alice!

Functions are defined with the function keyword. Parameters do not need type declarations (though they can have them).

Default parameters and type hints

function power(int $base, int $exp = 2): int {
    return $base ** $exp;
}
echo power(3);    // 9
echo power(3, 3); // 27

Type hints (int $base) force the argument to be that type, and : int declares the return type.

Variable scope

Variables defined outside a function are not available inside by default:

$prefix = "Hello";

function greet($name) {
    global $prefix;         // must declare global
    return "$prefix, $name!";
}

Better: pass variables as parameters instead of using global.

Anonymous functions / closures

$double = function($n) {
    return $n * 2;
};
echo $double(5);  // 10

// Arrow function (PHP 7.4+)
$triple = fn($n) => $n * 3;
echo $triple(5);  // 15

Common mistakes

  • Calling a function before it's defined — PHP does hoist function declarations
  • Forgetting to return a value — the function returns null
  • Using global when passing as a parameter is cleaner
  • Naming collisions with built-in PHP functions (always check the manual first)

Quick check below!

Next: Forms & Superglobals