using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Runtime.Serialization;

using System.Text;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

using System.Xml;

​

namespace ConsoleApplication2

{

    public class Program

    {

        public static void Main(string[] args)

        {

            string test = "(anything)....bbbbbb....(anything)";

            Regex r = new Regex("b(?=b)");

            var s = new System.Diagnostics.Stopwatch();

            s.Start();

            int i=0; 

            int l=5000;

            for (;i<l;i++) {

​

                var result = r.Matches(test);

            }

            Console.WriteLine(s.ElapsedTicks.ToString());

            i = 0;

            string needle = "bb"; 

            int pos = 0;

            s.Reset();

            s.Start();

            for (;i<l;i++) {

                pos = 0;

                while((pos = test.IndexOf(needle, pos)) != -1)

                {

                    pos++;

                }

            }

            Console.WriteLine(s.ElapsedTicks.ToString());

        }

    }

}

​