using System;

using System.Text.RegularExpressions;

using System.Diagnostics;

public class Program

{

    public static void Main()

    {

        var str = string.Concat(System.Linq.Enumerable.Repeat("1234567890", 2000));

        const int repeat = 1000;

        Stopwatch stopWatch = new Stopwatch();

        string str1;

        stopWatch.Start();

        for(int i = 0; i < repeat; i++)

            str1 = str.Replace("2"," ").Replace("7"," ");

        var elapsed = stopWatch.Elapsed;

        Console.WriteLine("String replace: " + elapsed);

        stopWatch.Restart();

        for(int i = 0; i < repeat; i++)

            str1 = str.Replace('2',' ').Replace('7',' ');

        elapsed = stopWatch.Elapsed;

        Console.WriteLine("Char replace:   " + elapsed);

​

        stopWatch.Restart();

        for(int i = 0; i < repeat; i++)

            str1 = Regex.Replace(str,"2|7"," ");

        elapsed = stopWatch.Elapsed;

        Console.WriteLine("Regex replace:  " + elapsed);

​

    }

}