How to split the string in c#

using System;
using System.Text.RegularExpressions;

class SplitStringTester {
    public string[] RegxSplit(string pattern, string input) {
        int i = 0;
        string[] arrRet = null;
        Regex rgx = new Regex(pattern, RegexOptions.IgnoreCase);
        MatchCollection matches = rgx.Matches(input);
        if (matches.Count > 0)
        {
            arrRet = new string[matches.Count];
            foreach(Match m in matches) {
                arrRet[i] = m.Value;
                i++;
            }
        }
        return arrRet;
    }

    public static void Main() {
        SplitStringTester tst = new SplitStringTester();
        string[] arrRet = tst.RegxSplit(@"(.{5})?", @"q2px1tfi9jNvrX07uxH78DUCzuXZKlwZjtN3iruaMi0=");
        if (arrRet != null) {
            Console.WriteLine("{0} ({1} matches):", @"q2px1tfi9jNvrX07uxH78DUCzuXZKlwZjtN3iruaMi0=", arrRet.Length);
            foreach (string sTok in arrRet)
                Console.WriteLine(sTok);
        }
        Console.ReadKey();
    }
}