php shopping cart

Hi guys,

I am currently in the process of making a shopping cart by following this tutorial - http://v3.thewatchmakerproject.com/journal/276/ . I am getting two errors when I follow this tutorial - Fatal error: Call to a member function query() on a non-object in includes/functions.inc.php on line 27 and - Undefined index: action. I have attached my code and if you could provide any help or feedback that would be greatly appreciated.

functions.inc.php:

<?php 
function writeShoppingCart() { 
    $cart = $_SESSION['cart']; 
    if (!$cart) { 
        return '<p>You have no items in your shopping cart</p>'; 
    } else { 
        // Parse the cart session variable 
        $items = explode(',',$cart); 
        $s = (count($items) > 1) ? 's':''; 
        return '<p>You have <a href="index.php?p=cart">'.count($items).' item'.$s.' in your shopping cart</a></p>'; 
    } 
} 

function showCart() { 
    global $db; 
    $cart = $_SESSION['cart']; 
    if ($cart) { 
        $items = explode(',',$cart); 
        $contents = array(); 
        foreach ($items as $item) { 
            $contents[$item] = (isset($contents[$item])) ? $contents[$item] + 1 : 1; 
        } 
        $output[] = '<form action="index.php?p=cart&?action=update" method="post" id="cart">'; 
        $output[] = '<table>'; 
        foreach ($contents as $id=>$qty) { 
            $sql = 'SELECT * FROM products WHERE prod_id = '.$id; 
            $result = $db->query($sql); 
            $row = $result->fetch(); 
            extract($row); 
            $output[] = '<tr>'; 
            $output[] = '<td><a href="index.php?p=cart&?action=delete&id='.$id.'" class="r">Remove</a></td>'; 
            $output[] = '<td>'.$product_name.' - '.$description.'</td>'; 
            $output[] = '<td>£'.$price.'</td>'; 
            $output[] = '<td><input type="text" name="qty'.$id.'" value="'.$qty.'" size="3" maxlength="3" /></td>'; 
            $output[] = '<td>£'.($price * $qty).'</td>'; 
            $total += $price * $qty; 
            $output[] = '</tr>'; 
        } 
        $output[] = '</table>'; 
        $output[] = '<p>Grand total: <strong>£'.$total.'</strong></p>'; 
        $output[] = '<div><button type="submit">Update cart</button></div>'; 
        $output[] = '</form>'; 
    } else { 
        $output[] = '<p>You shopping cart is empty.</p>'; 
    } 
    return join('',$output); 
} 
?> 

cart.php:

<?php 
if(!isset($_SESSION['username'])) {
echo "Welcome Guest!"; 
} else {
echo "<font color='red'>You are logged in as </font><font color='purple'>$_SESSION[username].</font><font color='orange'><a href='index.php?p=logout'>  logout?</a> </font><br><font color='red'>Dont forget $_SESSION[username]. always feel free to contact us for support when needed most</font><br><br>";
}
?>
<?php # main.inc.php 

/*  
 *    This is the main content module. 
 *    This page is included by index.php. 
 */ 

// Redirect if this page was accessed directly: 
if (!defined('BASE_URL')) { 

    // Need the BASE_URL, defined in the config file: 
    require_once ('../includes/config.inc.php'); 
     
    // Redirect to the index page: 
    $url = BASE_URL . 'index.php'; 
    header ("Location: $url"); 
    exit; 
     
} // End of defined() IF. 

// Include functions 
require_once('includes/functions.inc.php'); 
// Start the session 
// Process actions 
$cart = $_SESSION['cart']; 
$action = $_GET['action']; 
switch ($action) { 
    case 'add': 
        if ($cart) { 
            $cart .= ','.$_GET['id']; 
        } else { 
            $cart = $_GET['id']; 
        } 
        break; 
    case 'delete': 
        if ($cart) { 
            $items = explode(',',$cart); 
            $newcart = ''; 
            foreach ($items as $item) { 
                if ($_GET['id'] != $item) { 
                    if ($newcart != '') { 
                        $newcart .= ','.$item; 
                    } else { 
                        $newcart = $item; 
                    } 
                } 
            } 
            $cart = $newcart; 
        } 
        break; 
    case 'update': 
    if ($cart) { 
        $newcart = ''; 
        foreach ($_POST as $key=>$value) { 
            if (stristr($key,'qty')) { 
                $id = str_replace('qty','',$key); 
                $items = ($newcart != '') ? explode(',',$newcart) : explode(',',$cart); 
                $newcart = ''; 
                foreach ($items as $item) { 
                    if ($id != $item) { 
                        if ($newcart != '') { 
                            $newcart .= ','.$item; 
                        } else { 
                            $newcart = $item; 
                        } 
                    } 
                } 
                for ($i=1;$i<=$value;$i++) { 
                    if ($newcart != '') { 
                        $newcart .= ','.$id; 
                    } else { 
                        $newcart = $id; 
                    } 
                } 
            } 
        } 
    } 
    $cart = $newcart; 
    break; 
} 
$_SESSION['cart'] = $cart; 
?> 

    <h2>Your Shopping Cart</h2> 
    <?php echo writeShoppingCart(); ?> 
     
    <h2>Please Check Quantities</h2> 
    <p>Please check all the products with their quanitites and total and then please go to the checkout to buy your products</p> 
    <hr /> 
    <div id="cartdisplay"> 
    <?php echo showCart(); ?> 
    </div> 
    <hr /> 
    <p><a href="index.php">Back to Home Page!</a></p>