/*
 * Converts a date into day of week and number of days since
 * the start of 20th century.
 */

#include <stdio.h>

void main()
{
   int D, M, Y, Y_calc, year_quo, year_mod, month_ent[12] = {
       0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334    };

   long int day_century;

   char *name[] = {
       "Tuesday", "Wednesday", "Thursday", "Friday",
       "Saturday", "Sunday", "Monday"    };

   printf("Day: ");
   fflush(stdout);
   scanf("%d", &D);
   do {
      printf("Month: ");
      fflush(stdout);
      scanf("%d", &M);
      if (M < 1 || M > 12)
          fprintf(stderr,"Month 1-12 only\a\n");
   } while (M < 1 || M > 12);

   do {
      printf("Year: ");
      fflush(stdout);
      scanf("%d", &Y);
      if (Y < 1901)
         fprintf(stderr,"Year must be > 1900\a\n");
   } while (Y < 1901);


   Y_calc = Y - 1901;
   year_quo = Y_calc / 4;
   year_mod = Y_calc % 4;
   day_century = (long int)Y_calc * 365 + year_quo +
       month_ent[M - 1] + D;

   if (year_mod < 3 || M < 3)
      day_century--;

   printf("%d/%d/%d is %ld days after 1/1/1901 ", M, D, Y,
       day_century);
   printf("and it's a %s\n",name[day_century % 7]);
}