我在C＃中的销售订单无法正常工作

Question

  

可能重复：
  Qty Control in C#

我希望mods不介意重新发布这个。下面的代码不能按预期的方式工作。当最终用户点击btQty按钮时，数量变为-2。什么时候应该减少一个（因为销售）。这是代码，并提前感谢..

    cs.Open();
    int ret;
    string Query = "SELECT QTY from tblStock WHERE ID=1";
    SqlCommand cmd = new SqlCommand(Query, cs);
    string str = Convert.ToString(cmd.ExecuteScalar());
    if (str != "")
    {
        ret = Convert.ToInt32(cmd);
    }
    else
    {
        ret = -1; 
    }

    if (ret == 0)
    {
        lbqty.Text = "Not enough stocks.";
        dgUpdate();
    }

    else
    {
        cmd.CommandText = "UPDATE tblContacts SET QTY = QTY-1 WHERE ID=1";
        cmd.ExecuteNonQuery();
        if (ret == 1)
        {
            lbqty.Text = "Re-order. Remaining stocks: 1";
            dgUpdate();
        }
        else
        {
            txtQty.Text = "Remaining stocks: " + (ret - 1).ToString();
            lbqty.Text = "Remaining stocks: " + (ret - 1).ToString();
            dgUpdate();
        }
    }
    cs.Close();