C#

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="dir" value="\directory"/>
    <add key="fieldname1" value="\value1"/>
    <add key="fieldname2" value="\value2"/>
  </appSettings>
</configuration>

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="dir" value="\directory"/>
    <add key="fieldname1" value="\value1"/>
    <add key="fieldname2" value="\value2"/>
  </appSettings>
</configuration

using System;
using System.Xml;
using System.Configuration;
using System.Reflection;

using OpenNETCF.Configuration;
using System.Windows.Forms;

public class ConfigSettings
    {
        private ConfigSettings() { }

        public static string ReadSetting(string key)
        {
            return ConfigurationSettings.AppSettings[key];
        }

        public static void WriteSetting(string key, string value)
        {
            // load config document for current assembly
            XmlDocument doc = loadConfigDocument();

            // retrieve appSettings node
            XmlNode node = doc.SelectSingleNode("//appSettings");

            if (node == null)
                throw new InvalidOperationException("appSettings section not found in config file.");

            try
            {
                // select the 'add' element that contains the key
                XmlElement elem = (XmlElement)node.SelectSingleNode(string.Format("//add[@key='{0}']", key));
                if (elem != null)
                {
                    // add value for key
                    elem.SetAttribute("value", value);
                }
                else
                {
                    // key was not found so create the 'add' element 
                    // and set it's key/value attributes 
                    elem = doc.CreateElement("add");
                    elem.SetAttribute("key", key);
                    elem.SetAttribute("value", value);
                    node.AppendChild(elem);
                }
                doc.Save(getConfigFilePath());
            }
            catch
            {
                throw;
            }
        }

        public static void RemoveSetting(string key)
        {
            // load config document for current assembly
            XmlDocument doc = loadConfigDocument();

            // retrieve appSettings node
            XmlNode node = doc.SelectSingleNode("//appSettings");

            try
            {
                if (node == null)
                    throw new InvalidOperationException("appSettings section not found in config file.");
                else
                {
                    // remove 'add' element with coresponding key
                    node.RemoveChild(node.SelectSingleNode(string.Format("//add[@key='{0}']", key)));
                    doc.Save(getConfigFilePath());
                }
            }
            catch (NullReferenceException e)
            {
                throw new Exception(string.Format("The key {0} does not exist.", key), e);
            }
        }

        private static XmlDocument loadConfigDocument()
        {
            XmlDocument doc = null;
            try
            {
                doc = new XmlDocument();
                doc.Load(getConfigFilePath());
                return doc;
            }
            catch (System.IO.FileNotFoundException e)
            {
                throw new Exception("No configuration file found.", e);
            }
        }

        private static string getConfigFilePath()
        {
            return @"\Program Files\AppSetting.exe.xml";
        }
    }

class MyClass {

   private int x;
   private int y;

   public void doStuff() {
       x = y + 10;
   }

}

class MyClass {

   private int x;
   private int y;

   public int xProp {
      get {  return x;  }
      set {  this.x = value;  }
   }

   public int yProp {
      get {  return y;  }
      set {  this.y = value;  }
   }

   public void doStuff() {
       xProp = yProp + 10;
   }

}