"Claudia's Kids" wrox shopping tutorial: function updateCart() on a non-object

Code:
&lt;?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');



class Welcome extends CI_Controller {



 /**

  * Index Page for this controller.

  *

  * Maps to the following URL

  *   http://example.com/index.php/welcome

  * - or -  

  *   http://example.com/index.php/welcome/index

  * - or -

  * Since this controller is set as the default controller in 

  * config/routes.php, it's displayed at http://example.com/

  *

  * So any other public methods not prefixed with an underscore will

  * map to /index.php/welcome/<method_name>

  * @see http://ellislab.com/codeigniter/user-guide/general/urls.html

  *

  */



  function __construct()

  {

        // Call the Model constructor

        parent::__construct();

        $this->load->library('session');

        $this->load->library('cart');

  }



 public function index()

 {

    $data['title'] = "Welcome to Claudia's Kids";

    $data['navlist'] = $this->MCats->getCategoriesNav();

   $data['mainf'] = $this->MProducts->getMainFeature();

   $skip = $data['mainf']['id'];

   $data['sidef'] = $this->MProducts->getRandomProducts(3,$skip);

   $data['main'] = 'home';

    $this->load->vars($data);

    $this->load->view('template');

 }



  public function cat($id)

  {

  $cat = $this->MCats->getCategory($id);

    if (!count($cat))

    {

      redirect('welcome/index','refresh');

    }

    $data['title'] = "Claudia's Kids | ".$cat['name'];

    if ($cat['parentid'] < 1)

    {

      $data['listing'] = $this->MCats->getSubCategories($id);

      $data['level'] = 1;

    }

    else

    {

      $data['listing'] = $this->MProducts->getProductsByCategory($id);

      $data['level'] = 2;

    }

    $data['category'] = $cat;

    $data['main'] = 'category';

    $data['navlist'] = $this->MCats->getCategoriesNav();

   $this->load->vars($data);

    $this->load->view('template');

 }



  public function product($id)

  {

    $product = $this->MProducts->getProduct($id);

    if (!count($product))

    {

      redirect('welcome/index','refresh');

    }

    $data['grouplist'] = $this->MProducts->getProductsByGroup(3,$product['grouping'],$id);

    $data['product'] = $product;

    $data['title'] = "Claudia's Kids | ".$product['name'];

    $data['main'] = 'product';

    $data['navlist'] = $this->MCats->getCategoriesNav();

    $this->load->vars($data);

    $this->load->view('template');

 }



  public function cart($productid=0)

 {

    if ($productid > 0)

    {

      $fullproduct = $this->MProducts->getProduct($productid);

      $this->MOrders->updateCart($productid,$fullproduct);

      redirect('welcome/product/'.$productid, 'refresh');

    }

    else

    {

      $data['title'] = "Claudia's Kids | Shopping Cart";

      if (count($_SESSION['cart']) == true)

      {

        $data['main'] = 'shoppingcart';

        $data['navlist'] = $this->MCats->getCategoriesNav();

        $this->load->vars($data);

        $this->load->view('template');

      }

      else

      {

        redirect('welcome/index', 'refresh');

      }

    }

 }



  public function search()

  {

  if ($this->input->post('term'))

    {

      $data['results'] = $this->MProducts->search($this->input->post('term'));

    }

    else

    {

      redirect('welcome/index','refresh');

    }

    $data['main'] = 'search';

    $data['title'] = "Claudia's Kids | Search Results";

    $data['navlist'] = $this->MCats->getCategoriesNav();

    $this->load->vars($data);

    $this->load->view('template');

 }



  public function about_us()

 {

  $this->load->vars($data);

    $this->load->view('template');

 }



  public function privacy()

  {

    $this->load->vars($data);

    $this->load->view('template');

 }



}