protected void btn_AddCart_Click(object sender, EventArgs e) { Bookstore_BO bookstorebo = new Bookstore_BO(); productId = bookstorebo.retrieveProductId(lbl_Item.Text).ToString(); int OldQuantity = Convert.ToInt32(bookstorebo.retrieveProductQuantity(Convert.ToInt32(productId))); int NewQuantity = OldQuantity - Convert.ToInt32(TB_Quantity.Text); if (NewQuantity >= 0) { int IdExist = Convert.ToInt32(bookstorebo.retrieveProductIdFromCart(Convert.ToInt32(productId))); if (IdExist > 0) { bookstorebo.updateQuantityInCartDB(Convert.ToInt32(productId), Convert.ToInt32(TB_Quantity.Text)); } else { ImageURL = bookstorebo.retrieveImageString(Convert.ToInt32(productId)); NAME = GridView1.SelectedRow.Cells[2].Text.ToString(); PRICE = Convert.ToDecimal(GridView1.SelectedRow.Cells[3].Text); Quantity = Convert.ToInt32(TB_Quantity.Text.Trim()); bookstorebo.AddProduct(Convert.ToInt32(productId), ImageURL, NAME, PRICE, Quantity); } } else { lbl_Error.Visible = true; } lbl_Item.Text = ""; TB_Quantity.Text = ""; lbl_Success.Visible = true; }