Class definition and usage

A class is a collection of variables and functions working with these variables. Variables are defined by var and functions by function. A class is defined using the following syntax:

class Cart {
    var $items;  // Items in our shopping cart

    // Add $num articles of $artnr to the cart

    function add_item($artnr, $num) {
        $this->items[$artnr] += $num;
    }

    // Take $num articles of $artnr out of the cart

    function remove_item($artnr, $num) {
        if ($this->items[$artnr] > $num) {
            $this->items[$artnr] -= $num;
            return true;
        } elseif ($this->items[$artnr] == $num) {
            unset($this->items[$artnr]);
            return true;
        } else {
            return false;
        }
    }
}
?>

This defines a class named Cart that consists of an associative array of articles in the cart and two functions to add and remove items from this cart.