Now, here's a program for calculating the date of Easter.

[Commie Pinko Dirtbag]

Adapted the mechanism showed here: http://en.wikipedia.org/wiki/Computus#Meeus.2FJones.2FButcher_Gregorian_algorithm

Save the text below as easter.c and, under Linux or Mac OS, compile like this: "gcc -DSTANDALONE -Wall -o easter easter.c"

It should also compile as a console program under Visual C++. I suppose.

Programmer types can use it as a library, by not defining STANDALONE.

"easter", on its own, prints this year's Easter. For other years, use "easter 2009", "easter 1993" etc.

#include <time.h>

#ifdef STANDALONE
#include <stdio.h>
#include <stdlib.h>
#endif

void easter(int year, int *month, int *day)
{
        int a, b, c, d, e, f, g, h, i, k, l, m;

        a = year % 19;
        b = year / 100;
        c = year % 100;
        d = b / 4;
        e = b % 4;
        f = (b + 8) / 25;
        g = (b - f + 1) / 3;
        h = (19 * a + b - d - g + 15) % 30;
        i = c / 4;
        k = c % 4;
        l = (32 + 2 * e + 2 * i - h - k) % 7;
        m = (a + 11 * h + 22 * l) / 451;
        *month = (h + l - 7 * m + 114) / 31;
        *day = ((h + l - 7 * m + 114) % 31) + 1;
}

#ifdef STANDALONE
int main (int argc, char **argv)
{
        int myyear, mymonth, myday;
        time_t now;
        struct tm localnow;

        if (argc < 2)
        {
                time(&now);
                localtime_r(&now, &localnow);
                myyear = localnow.tm_year + 1900;
        }
        else
                myyear = atoi(*(argv + 1));

        easter(myyear, &mymonth, &myday);
        printf("%d/%d/%d\n", myyear, mymonth, myday);

        return 0;
}
#endif

EDIT: the above is in the public domain.

[yvr girl]

1. way back in the stone ages, I made a perpetual calendar

for my programming class. Easter was the trickiest part.