using System;

using System.Linq;

using System.Collections;

using System.Collections.Generic;

using System.Xml;

using System.Xml.Linq;

​

public class Program

{

    public static void Main()

    {

        string s = @"<connectionStrings>    <add name=""SqlServer""              connectionString=""Data Source=192.168.1.1; Initial Catalog=s; Application Name=s; MultipleActiveResultSets = true; Pooling=True; User ID=1111;Password=1111;"" />           <add name=""SqlServer_WinAuthentication""             connectionString=""Data Source=.; Initial Catalog=MeterShop; Integrated Security=True; Application Name=MeterShop; MultipleActiveResultSets = true; Pooling=True;"" />    <add name=""SqlServer_SqlAuthentication""             connectionString=""Data Source=.; Initial Catalog=MeterShop; User ID=1; Password=1; Application Name=1; MultipleActiveResultSets = true; Pooling=True;"" /></connectionStrings>";

        XDocument doc = XDocument.Parse(s);

        var target = doc.Descendants("connectionStrings")   

                        .SingleOrDefault(e => e.Element("add").Attribute("name").Value == "SqlServer");                   

        Console.WriteLine(target.Element("add").Attribute("name").Value);

        target.Element("add").Attribute("name").Value = "any thing you want";

        //doc.Save("filename");

​

    }

}

​

​