مساعدة فى معرفة خطا فى الكود

السلام عليكم

انا عاملة صفحة موجود فيها منتجات وكل منتج موجود جانبه  (add to card) لما بضغط عليه بيروح لصفحة (shopping cart) وبينفذ اللى انا عايزه بس المشكله انه بيطلع خطا فيا ريت لوحد يعرف ايه الخطا يقولى عليه

دى صفحة  shopping cart)

<?php
 include("includes/db.php");
 include("includes/functions.php");
 
 if($_REQUEST['command']=='delete' && $_REQUEST['pid']>0){
  remove_product($_REQUEST['pid']);
 }
 else if($_REQUEST['command']=='clear'){
  unset($_SESSION['cart']);
 }
 else if($_REQUEST['command']=='update'){
  $max=count($_SESSION['cart']);
  for($i=0;$i<$max;$i++){
   $pid=$_SESSION['cart'][$i]['productid'];
   $q=intval($_REQUEST['product'.$pid]);
   if($q>0 && $q<=999){
    $_SESSION['cart'][$i]['qty']=$q;
   }
   
  }
 }

?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Shopping Cart</title>
<script language="javascript">
 function del(pid){
  if(confirm('Do you really mean to delete this item')){
   document.form1.pid.value=pid;
   document.form1.command.value='delete';
   document.form1.submit();
  }
 }
 function clear_cart(){
  if(confirm('This will empty your shopping cart, continue?')){
   document.form1.command.value='clear';
   document.form1.submit();
  }
 }
 function update_cart(){
  document.form1.command.value='update';
  document.form1.submit();
 }

</script>
</head>

<body>
<form name="form1" method="post"  >
<input type="hidden" name="pid" />
<input type="hidden" name="command" />
 <div style="margin:0px auto; width:600px;" >
    <div style="padding-bottom:10px">
     <h1 align="center">Your Shopping Cart</h1>
    <input type="button" value="Continue Shopping" onclick="window.location='clothes.php'" />
    </div>
     <div style="color:#F00"></div>
     <table border="0" cellpadding="5px" cellspacing="1px" style="font-family:Verdana, Geneva, sans-serif; font-size:11px; background-color:#E1E1E1" width="100%">
     <?php
   if(is_array($_SESSION['cart'])){
             echo '<tr bgcolor="#FFFFFF" style="font-weight:bold"><td>Serial</td><td>Name</td><td>Price</td><td>Qty</td><td>Amount</td><td>Options</td></tr>';
    $max=count($_SESSION['cart']);
    for($i=0;$i<$max;$i++){
     $pid=$_SESSION['cart'][$i]['productid'];
     $q=$_SESSION['cart'][$i]['qty'];
     $pname=get_product_name($pid);
     if($q==0) continue;
   ?>
              <tr bgcolor="#FFFFFF"><td><?php echo $i+1?></td><td><?php echo $pname?></td>
                    <td>$ <?php echo get_price($pid)?></td>
                    <td><input type="text" name="product<?php echo $pid?>" value="<?php echo $q?>" maxlength="3" size="2" /></td>                   
                    <td>$ <?php echo get_price($pid)*$q?></td>
                    <td><a href="javascript:del(<?php echo $pid?>)">Remove</a></td></tr>
            <?php     
    }
   ?>
    <tr><td><b>Order Total: $<?php echo get_order_total()?></b></td><td colspan="5" align="right"><input type="button" value="Clear Cart"  onclick="clear_cart()"><input type="button" value="Update Cart"  onclick="update_cart()"><input type="button" value="Place Order"  onclick="window.location='billing.php'"></td></tr>
   <?php
            }
   else{
    echo "<tr bgColor='#FFFFFF'><td>There are no items in your shopping cart!</td>";
   }
  ?>
        </table>
    </div>
</form>
</body>
</html>