我的销售控制器代码出了什么问题？

Question

undefined variable productdata, I dont knw what's happening with my code

 case 'add_sale':
    if (isset($_POST['select_product']) && $_POST['select_product']!= '' 
         && isset($_POST['txt_amount']) && $_POST['txt_amount']!= 0 ){

        $product = new product();
        $productarr = $product->getProductById($_POST['select_product']);
        foreach($productarr as $data){
          $operation = $data[2]*$_POST['txt_amount'];
          $subtotal  = number_format($operation,2);
          $productdata = array(
                          'idproduct'=>$data[0],
                          'product'=>$data[1],
                          'price'=>$data[2],
                          'amount'=>$_POST['txt_amount'],
                          'subtotal'=>$subtotal
                         );
        }
        $_SESSION['detalle'][] = $productdata;
        echo "success";
    }else{
        echo 'something went wrong';
    }
    break;

Answer 1

declare $productdata = array(); just inside the 1st if() block. Actually, when your $productarr will blank, it will never enter your foreach() so at that time $productdata in undefined variable