public void ddlProduct_SelectedIndexChanged(object sender, EventArgs e)
    {
        CustomerENT entCustomer = new CustomerENT();
        CustomerBAL balCustomer = new CustomerBAL();

        if (ddlProductID.SelectedIndex > 0)
        {
            DataTable dt = balCustomer.SelectProductAmount(Convert.ToInt32(ddlProductID.SelectedValue));

            if (dt != null && dt.Rows.Count > 0)
            {
                foreach (DataRow dr in dt.Rows)
                {
                    if (!dr["BottlePrice"].Equals(DBNull.Value))
                    {
                        txtAmount.Text = Convert.ToDecimal(dr["BottlePrice"]).ToString();
                    }
                }
            }
        }
    }