gistfile1.txt

case "1":
    Console.WriteLine("Select which of the following to add to cart by entering it's number:");
    foreach (var product in result)
    {
        Console.WriteLine(" {0}. {1}, Stock: {2}, Price: {3}", product.RecordNumber, product.Name, product.Stock, product.Price);
    }

    int ProductInput = Convert.ToInt32(Console.ReadLine());

    // answer..
    var selectedProduct = result.Single(product => product.RecordNumber == ProductInput);
    ShoppingCart.AddProduct(selectedProduct);

    var productElement =
        (from descendant in XDoc.Descendants("product")
         where descendant.Element("recordNumber").Value == ProductInput.ToString()
         select descendant).Single();

    var stock = Convert.ToInt32(productElement.Element("stock").Value);
    productElement.Element("stock").Value = (stock - 1).ToString();
    XDoc.Save("inventory.xml");


    break;