select ()
{
  case month == 1 | month == 3 | month == 5 | month == 7 | month == 8 | month == 10 | month == 12:
  return 31;

  case month == 4 | month == 6 | month == 9 | month == 11:
  return 30;

  case month == 2:
  return 28;
}
else
{
  error (ERR_PARAMETER);
}