C# Code to Find Count of Sub-string Occurrences

string MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
string stringToFind = "OU=";

List<int> positions = new List<int>[];
int pos = 0;
while ((pos < MyString.Length) && (pos = MyString.IndexOf(stringToFind, pos)) != -1)
{
    positions.Add(pos);
    pos += stringToFind.Length();
}

Console.WriteLine("{0} occurrences", positions.Count);
foreach (var p in positions)
{
    Console.WriteLine(p);
}

var matches = Regex.Matches(MyString, "OU=");
Console.WriteLine("{0} occurrences", matches.Count);
foreach (var m in matches)
{
    Console.WriteLine(m.Index);
}