using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string input = "this is a test";
string pattern = "is?";
Match match = Regex.Match(input, pattern);
while (match.Success)
{
Console.WriteLine("'{0}' found in the source code at position {1}.",
match.Value, match.Index);
match = match.NextMatch();
}
}
}