/********************************************************************
 *                                                                  *
 *     This program calculates the Eastern Orthodox Easter Day      *
 *     for any year between 1753 and 4000. Translated to C from     *
 *     a program in Pascal posted to bit.listserv.hellas by         *
 *     Apostolos Syropoulos, it comes with no warranty whatsoever.  *
 *                                                                  *
 *             Pascalis Ligdas,  one humid day, Aug. 1993           *
 *                     U.of Md. College Park                        *
 *                                                                  *
 ********************************************************************/

#include <stdio.h>

#define iabs(x)   ((x>=0)?(x):(-x))

int year, epakti, month, fullmoon, Easter, fullmoonday;

int daynumber(dd,mm,yy)
     int  dd, mm, yy;
{
  int  yearincentury, century;
  int  day, month, year;

  month = mm; year = yy; day = dd;
  century = year/100;
  yearincentury = year%100;
  if(month>=3) {
    month-=2;
  }
  else {
    month+=10;
    if(yearincentury>0) {
      yearincentury--;
    }
    else {
      yearincentury = 99;
      century--;
    }
  }
  return(((int)(2.61*month-0.2)+day+yearincentury+
          century/4+yearincentury/4-2*century) % 7);

  /* if daynumber=0 then day is Sunday, */
  /* if daynumber=1 then day is Monday, etc. */
}

main()

{   
  printf("\nEastern Orthodox Easter Day Calculation Program.\n");
  do {
    printf("Enter year...");
    scanf("%d", &year);
  }while((year<1753)&&(year>4000));
  epakti = (((year-2)%19) * 11) % 30;
  printf("\epakti: %d\n",epakti);
  if(epakti>23) {
    month = 4;
  }
  else {
    month = 3;
  }
  fullmoon = 44 - epakti + 13;
  if((month==4)&&(fullmoon>30)) {
    month++;
    fullmoon-=30;
  }
  else if((month==3)&&(fullmoon>31)) {
    month++;
    fullmoon-=31;
  }
  fullmoonday = iabs(daynumber(fullmoon,month,year));
  switch(fullmoonday){
  case 0: Easter = fullmoon+7;break;
  case 1: Easter = fullmoon+6;break;
  case 2: Easter = fullmoon+5;break;
  case 3: Easter = fullmoon+4;break;
  case 4: Easter = fullmoon+3;break;
  case 5: Easter = fullmoon+2;break;
  case 6: Easter = fullmoon+1;break;
  }
  if((month==3)&&(Easter>31)) {
    month++;
    Easter-=31;
  }
  else if((month==4)&&(Easter>30)) {
    month++;
    Easter-=30;
  }
  printf("\nEaster date : %d-%d-%d\n", Easter, month, year);
}