php - Adding items to shopping basket using sessions -

this shopping basket , user can click add basket passing action=add variable across , selected switch statement. first time add item causes error (bottom). occurs first time leads me believe because session[cart] has not been created.

the variables set here:

if(isset($_get['id']))  { $item_id = $_get['id'];//the product id url  $action = $_get['action'];//the action url  }  else { $action = "nothing"; }     <?php  if(empty($_session['user_loggedin'])) {  header ('location: logon.php'); } else {  switch($action) { //decide       case "add":         $_session['cart'][$item_id]++; //add 1 quantity of product id $product_id      break;      case "remove":         $_session['cart'][$item_id]--; //remove 1 quantity of product id $product_id          if($_session['cart'][$item_id] == 0) unset($_session['cart'][$item_id]); //if quantity zero, remove (using 'unset' function) - otherwise show zero, -1, -2 etc when user keeps removing items.      break;      case "empty":         unset($_session['cart']); //unset whole cart, i.e. empty cart.      break;      case "nothing":     break; }  if(empty($_session['cart'])) {  echo "you have no items in shopping cart."; } 

adding items working fine first time add empty basket error below:

notice: undefined index: cart in h:\student\s0190204\ggj\basket.php on line 57 notice: undefined index: 1 in h:\student\s0190204\ggj\basket.php on line 57 

that because $_session['cart'] variable isn't initialized first request. try below.

if(empty($_session['user_loggedin'])) {  header ('location: logon.php'); } else {     // added this...    if(empty($_session['cart'])){        $_session['cart'] = array();    }  switch($action) { //decide       case "add":         $_session['cart'][$item_id]++; //add 1 quantity of product id $product_id      break;      case "remove":         $_session['cart'][$item_id]--; //remove 1 quantity of product id $product_id          if($_session['cart'][$item_id] == 0) unset($_session['cart'][$item_id]); //if quantity zero, remove (using 'unset' function) - otherwise show zero, -1, -2 etc when user keeps removing items.      break;      case "empty":         unset($_session['cart']); //unset whole cart, i.e. empty cart.      break;      case "nothing":     break; }  if(empty($_session['cart'])) {  echo "you have no items in shopping cart."; }