using System;

using System.Linq;

using System.Diagnostics;

using System.Text;

public class Program

{

    public static void Main()

    {

        var ss = Enumerable.Range(1, 10000).Select(_ => new { s1 = Guid.NewGuid().ToString(), s2 = Guid.NewGuid().ToString()}).ToList();

        var sw = Stopwatch.StartNew();

        ss.ForEach(_ => Add2(_.s1, _.s2));

        Console.WriteLine("String Builder: {0}", sw.Elapsed);

        sw = Stopwatch.StartNew();

        ss.ForEach(_ => Add1(_.s1, _.s2));

        Console.WriteLine("String  Concat: {0}", sw.Elapsed);

    }

    static string Add1(string s1, string s2) { return s1 + s2; }

    static string Add2(string s1, string s2)

    {

        var sb = new StringBuilder();

        sb.Append(s1);

        sb.Append(s2);

        return sb.ToString();

    }

}