/*****
                              datename()

      This function returns the day of the week for a date. It is based
   on Zeller's Congruence.

   Argument list:    int month      the month
                     int day        the day
                     int year       the year

   Return value:     char *         a pointer to the day of the week

*****/

char *datename(int day, int month, int year)
{
   static char *days[] = {"Sun.", "Mon.", "Tues", "Wed.",
                          "Thur", "Fri.", "Sat.", "Sun."};

   int index;

   if (year < 100)         /* If century is missing         */
      year += 1900;

   if (month > 2) {        /* Everything is from February   */
      month -= 2;
   } else {
      month += 10;
      year--;
   }

   index = ((13 * month - 1) / 5) + day + (year % 100) + ( (year % 100) / 4)
           + ((year / 100) / 4) - 2 * (year / 100) + 77;
   index = index - 7 * (index / 7);

   return days[index];
}