public static string RemoveSpecialCharacters(string str) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < str.Length; i++) { if ((str[i] >= '0' && str[i] <= '9') || (str[i] >= 'A' && str[i] <= 'z' || (str[i] == '.' || str[i] == '_'))) { sb.Append(str[i]); } } return sb.ToString(); }