php - Add-to-cart coding is that correct with form? -

<?php session_start(); include("conn.php");  $action = $_post['action']; $user = $_session['username'];  if(empty($user)){ echo"<script>alert('please log in!');window.location='log in.php';</script>"; exit; }  if($action == 'add'){ $cart_arr = array(   'foodid'=>$_post['foodid'],   'order_num'=>$_post['order_num'],   'food_type'=>$_post['food_type'],   );    $cart_session = $_session['cart_'.$user];   if(empty($cart_session)){       $cart_session[$cart_arr['foodid']] = $cart_arr;   } else if(!empty($cart_session[$cart_arr['foodid']])){       $cart_session[$cart_arr['foodid']]['order_num']+=$cart_arr['order_num'];   } else {       echo $cart_session[$cart_arr['foodid']] = $cart_arr;   }    $_session['cart_'.$user] = $cart_session;   } else if($action == 'clear'){       $_session['cart_'.$user]=array();       echo"<script>alert('shopping cart empty, return home!');window.location='homepage.php';</script>";       exit;    } else if($action == 'change'){       $temp_cart = $_session['cart_'.$user];       foreach($temp_cart $k=>$v){           if($_post['goods_'.$k]!= $v['order_num']){               $temp_cart[$k]['order_num'] = $_post['goods_'.$k];           }      if($_post['goods_'.$k] == 0){         unset($temp_cart[$k]);     }    }     $_session['cart_'.$user] = $temp_cart;    }     if(empty($_session['cart_'.$user])){        echo"<script>alert('shopping cart empty, please add orders!');window.location = 'homepage.php';</script>";      exit;  }   $goods_id = array();  $cart = $_session['cart_'.$user];  $v['food_type'] = $_post['food_type'];  foreach($cart $k=>$v){      $goods_id[$v['foodid']] = $v['foodid'];  }   $goods_id_str = implode(",",$goods_id);  mysql_query("set names utf8");  $sql = "select * foodmenu foodid in (".$goods_id_str.")";  $query = mysql_query($sql);  $cart_goods = array();  while($arr = mysql_fetch_array($query)){      $cart_goods[$arr['foodid']] = $arr;  }   foreach($cart $k=>$v){      $cart[$k]['food_name'] = $cart_goods[$k]['food_name'];      $cart[$k]['food_img'] = str_replace("../","",$cart_goods[$k]['food_img']);      $cart[$k]['food_price'] = $cart_goods[$k]['food_price'];      $cart[$k]['food_description'] = $_post['food_description'];  }  ?> 

may know coding correct? because shows blank page when click on button on previous php add-to-cart purpose , shows normal header @ top. attach form access php.

<div class="detailtop">     <?php              $result = mysql_query("select * foodmenu foodid = '$foodid'");          while($row=mysql_fetch_array($result)){              ?>         <dl>             <dt>             <img src="<?php echo  $row["food_img"];?>" /> </dt>             <dd>     <form action="order.php" method="get" name="send" onsubmit="return check()"  enctype="multipart/form-data">                 <h3><?php echo  $row["food_name"];?></h3>                 <div class="detailtips">                     <?php echo  $row["food_description"];?>                 </div>                 <p><span>restaurant:</span><strong><?php echo  $row["restaurant_name"];?></strong></p>                 <p><span>type :</span><strong><?php echo  $row["food_type"];?></strong></p>                 <p><span>price :</span>rm &nbsp;<strong><?php echo  $row["food_price"];?><input name="num"  type="hidden" class="num" value="<?php echo  $row["food_price"];?>" /></strong></p>                  <div class="order" style=" padding-top:20px; padding-left:20px;">                 <input name="id" type="hidden" value="<?php echo  $row["foodid"];?>" />                 <input name="" type="submit"  value="" class="ordersubmit" style=" margin-left:30px; margin-top:20px;">                 </div>                 </form>             </dd>         </dl>         <?php }?>     </div>