using System;using System.Text.RegularExpressions;public class Test
...{
public static void Main ()
...{ // Define a regular expression for repeated words. Regex rx = new Regex(@"(?<word>w+)s+(k<word>)", RegexOptions.Compiled | RegexOptions.IgnoreCase); // Define a test string. string text = "The the quick brown fox fox jumped over the lazy dog dog."; // Find matches. MatchCollection matches = rx.Matches(text); // Report the number of matches found. Console.WriteLine("{0} matches found.", matches.Count); // Report on each match. foreach (Match match in matches) ...{ string word = match.Groups["word"].Value; int index = match.Index; Console.WriteLine("{0} repeated at position {1}", word, index); 
} } 
}http://www.microsoft.com/china/msdn/library/webservices/asp.net/regexnet.mspx?mfr=true