c sharp simple operation on xml

The xml file format is as follows:  
< ?xml   version="1.0"   encoding="utf-8"? >  
< userdata   createuser="false" >  
< dataconnection >  
< server > localhost < /server >  
< uid > sa < /uid >  
< pwd > < /pwd >  
< /dataconnection >  
< net >  
< name > jiayuan < /name >  
< /net >  
< /userdata >  

Read a property  
in the node XmlDocument   doc=new   XmlDocument();  
doc. Load (" config xml "); // you can add paths like D:\ config.xml  
XmlNode   xnuser=doc.SelectSingleNode("userdata");  
string   flag=xnuser.Attributes["createuser"].InnerText;  

Read the value  
from the node XmlDocument   doc=new   XmlDocument();  
doc.Load("config.xml");  
XmlNode   xnserver   =   doc.SelectSingleNode("userdata/dataconnection/server");  

Modify the node's properties  
XmlDocument   doc=new   XmlDocument();  
doc.Load("config.xml");  
XmlNode   xnuser=doc.SelectSingleNode("userdata");  
xnuser.Attributes["createuser"].InnerText="false";  
doc.Save("config.xml");  

Append node  
XmlDocument   doc   =   new   XmlDocument();  
XmlTextReader   reader   =   new   XmlTextReader("config.xml");  
doc.Load("config.xml");  
XmlElement   root   =   doc DocumentElement;   //   gets the root node  
XmlElement   tagMessage   =   doc.CreateElement("net");  
XmlElement   tagText   =   doc.CreateElement("name");  
tagText.InnerText   =   netname;  
tagMessage. AppendChild (tagText);   //   is appended to the end of   xml   text  
root.AppendChild(tagMessage);  
reader. Close ();   //   close   XmlTextReader  
doc. Save (" config xml ");   //   save   xml