/* File: thanks.c
   This program determines the date of Thanksgiving
   on any given year, after 1900.
*/

#include <stdio.h>
#include "genlib.h"
#include "simpio.h"
#include "calendar.h"

main() {
  int year, month, i, first_thursday ;
  int start, this_month_days, turkey_day ;

  /* get year from user */
  printf("year =? ") ;
  year = GetInteger() ;
  printf("\n") ;

  /* January 1900, starts on Monday */
  start = 1 ;

  /* Calculate weekday of January 1 */
  for (i = 1900; i < year ; i++) {
     start = AddDay(start, YearDays(i)) ;
  }

  /* Caluculate weekday of November 1 */
  for (month = 1 ; month < 11 ; month++) {
      this_month_days = MonthDays(month, year) ;
      start = AddDay(start, this_month_days) ;
  }

  /* Calculate date of first Thursday */
  if (start <= Thursday) {
     first_thursday = Thursday - start + 1 ;
  } else {
     first_thursday = Thursday - start + 1 + 7 ;
  }
  turkey_day = first_thursday + 21 ;

  printf("In %d, Thanksgiving is on November %d.\n",
     year, turkey_day) ;
  printf("\n   November %d\n", year) ;
  printf(" Su  M Tu  W Th  F Sa\n") ;
  PrintOneMonth(start, 30) ;
}