using System;

using System.Text.RegularExpressions;                   

public class Program

{

    public static void Main()

    {

        string no = "[0-9]+(?:[\\.,][0-9]*)?";

        Regex regex = new Regex(@"(?:\s+" + no + @"(\s*)([xX\*])\1" + no + @"(?:\1\2\1" + no + @")*\s+)|(?:\s+" + no + @"(?:\s+" + no + @")+\s+)");

        string test = " 10 x 3 ";

         MatchCollection matches = regex.Matches(test);

        // Report the number of matches found.

        Console.WriteLine("{0} matches found in:\n   {1}",

                          matches.Count,

                          test);

        Console.WriteLine(regex);

    }

}