using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Xml.Serialization;

using System.Xml;

using System.IO;

using System.Diagnostics;

using System.Xml.Linq;

using System.Xml.Schema;

using System.Xml.XPath;

​

​

    public class TestClass

    {

        static string GetXml()

        {

            var xml = @"<Order 

    CallConfirm=""1""

    PayMethod=""Безнал"" 

    QtyPerson=""2"" 

    Type=""2"" 

    PayStateID=""0"" 

    Remark=""111111"" 

    RemarkMoney=""0"" 

    TimePlan="""" 

    Brand=""1"" 

    DiscountPercent=""0"" 

    BonusAmount=""0""

    Department="""">

       <Customer Login=""dev.bohdan@gmail.com"" FIO=""Bohdan Trachuk""/>

       <Address 

          CityName=""Київ"" 

          StationName="""" 

          StreetName="""" 

          House="""" 

          Corpus="""" 

          Building="""" 

          Flat="""" 

          Porch="""" 

          Floor="""" 

          DoorCode=""""/>         

       <Phone Code="" (0"" Number=""96) 717-19-02"" />

       <Products/>

</Order>";

            return xml;

        }

​

        public static void Test()

        {

            var xml = GetXml();

​

            var doc = XDocument.Parse(xml);

​

            var counttextText = "3";

            var Code1 = "code1";

​

            var product = new XElement("Product", new XAttribute("Code", Code1), new XAttribute("Qty", counttextText));

            var products = doc.Descendants("Products").First(); // Get the first Products node.  Throw an exception if not found.

            products.Add(product);

            ConsoleAndDebug.WriteLine(doc);

        }

    }

​

    public static class ConsoleAndDebug

    {

        public static void WriteLine(object s)

        {

            Console.WriteLine(s);

            Debug.WriteLine(s);

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            TestClass.Test();

        }

    }