XML C#

using System;
using System.IO;
using System.Xml;
public class Sample
{
  private const string filename = "sampledata.xml";
  public static void Main()
  {
     XmlTextWriter writer = new XmlTextWriter (filename, null);
     writer.Formatting = Formatting.Indented;
     writer.WriteComment("sample XML fragment");
     writer.WriteStartElement("bookstore");
     writer.WriteAttributeString("xmlns", "bk", null, "urn:samples");
     writer.WriteStartElement("book");
     string prefix = writer.LookupPrefix("urn:samples");
     writer.WriteStartAttribute(prefix, "ISBN", "urn:samples");
     writer.WriteString("1-111111-11");
     writer.WriteEndAttribute();     
     writer.WriteStartElement("title");
     writer.WriteString("C#");
     writer.WriteEndElement();
     writer.WriteElementString("price", "19.95");
     writer.WriteStartElement(prefix, "style", "urn:samples");
     writer.WriteString("hardcover");
     writer.WriteEndElement();
     writer.WriteEndElement();
     writer.WriteEndElement();
     writer.Flush();
     writer.Close();
     XmlDocument doc = new XmlDocument();
     doc.PreserveWhitespace = true;
     doc.Load(filename);
     Console.Write(doc.InnerXml);  
  }
}