@toth said:This is clearly done the wrong way. The sensible solution to this problem would be: string digits = "0123456789";foreach(char c in fphone) { if(digits.IndexOf(c.ToString()) < 0) { fphone = ""; break; }}  Sadly, I think this performs better than the regex.The non-retarded way of doing it is s = s.Any(c => !char.IsDigit(c)) ? "" : s (Sorry for being too on-topic, but the actual code WTFery in this thread was just too egregious)