PHP Functions

A function is a block of code with a name. You write it once and use it as many times as you like.

Built-in Functions

PHP already has thousands of functions, such as strlen(), date() and count(). In this lesson you will write your own.

Creating a Function

<?php
function greet() {
    echo "Welcome to Workownix!<br>";
}

greet();
greet();

Welcome to Workownix!
Welcome to Workownix!

The code inside the function only runs when you call it with greet().

Parameters

Parameters let you send values into a function:

<?php
function greetStudent($name, $course) {
    echo "Hello $name, welcome to the $course course.<br>";
}

greetStudent("Ali", "Web Development");
greetStudent("Ayesha", "Graphic Designing");

Hello Ali, welcome to the Web Development course.
Hello Ayesha, welcome to the Graphic Designing course.

Default Values

A parameter can have a default value, used when you do not pass one:

<?php
function deliveryCharge($city = "Karachi") {
    return $city === "Karachi" ? 150 : 300;
}

echo deliveryCharge() . "<br>";
echo deliveryCharge("Multan");

150
300

Returning Values

return sends a value back to the code that called the function:

<?php
function totalBill($price, $qty, $discount = 0) {
    $total = $price * $qty;
    return $total - ($total * $discount / 100);
}

$bill = totalBill(500, 3, 10);
echo "You pay Rs $bill";

You pay Rs 1350

Type Declarations

Modern PHP lets you say which types a function accepts and returns. PHP then checks the values for you.

<?php
declare(strict_types=1);

function average(int ...$numbers): float {
    return array_sum($numbers) / count($numbers);
}

echo average(70, 80, 95);

81.666666666667

int ...$numbers collects any number of integer arguments into an array. With strict_types=1, passing "70" (a string) would cause an error.

Named Arguments (PHP 8)

You can pass arguments by name, in any order:

<?php
function makeLabel(string $text, bool $bold = false, string $color = "black"): string {
    return "$text ($color" . ($bold ? ", bold" : "") . ")";
}

echo makeLabel("Sale", color: "red");

Sale (red)

Arrow Functions

A short function for simple, one-line jobs:

<?php
$addTax = fn($price) => $price * 1.18;
echo $addTax(1000);

1180

Variable Scope

Variables created inside a function exist only inside it. Variables from outside are not visible inside, unless you pass them as parameters.

Exercise