protected void btnUpdateCart_Click(object sender, EventArgs e) { // Connect to the database DatabaseMgmt objdbMgmt = new DatabaseMgmt(); string strSqlCmd; // Iterate through all rows within shopping cart list // (i.e. the dgShopCart data grid) int i; for (i = 0; i <= dgShopCart.Rows.Count - 1; i++) { // Obtain references to row's controls TextBox txtQuantity; txtQuantity = (TextBox)dgShopCart.Rows[i].FindControl("txtQty"); // Get the quantity value from textbox // and convert to integer int intQuantity; intQuantity = Convert.ToInt16(txtQuantity.Text); if (intQuantity <= 0) { Response.Write("<script>alert('Invalid quantity');</script>"); return; } // Get the ProductId from the first cell // and convert to integer int intProductID; intProductID = Convert.ToInt16(dgShopCart.Rows[i].Cells[0].Text); strSqlCmd = $"select quantity from Product where productId = {intProductID}"; SqlDataReader dR = objdbMgmt.ExecuteSelect(strSqlCmd); if (dR.Read()) { if (intQuantity > int.Parse(dR["quantity"].ToString())) { Response.Write("<script>alert('Invalid quantity');</script>"); return; } } objdbMgmt.Close(); // Update quantity order of shopping cart in database strSqlCmd = "UPDATE ShopCartItem SET Quantity=" + intQuantity + " WHERE ShopCartID=" + Session["ShopCartID"] + " AND ProductId=" + intProductID; objdbMgmt.Open(); objdbMgmt.ExecuteNonQuery(strSqlCmd); } displayShopCart(); objdbMgmt.Close(); }