h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is standard, portable C that will use the algorithim detailed above.

*****

#include

void calcEaster(int year, int *month, int *day);

int main (int argc, const char * argv[])
{
int year, month, day;

printf("Calculates the month and day of easter on given year.\n");

printf("Enter a year between 1700 and 2299: ");
fflush(stdout);
scanf("%i", &year);

if (year < 1700 || year > 2299)
printf("WARNING: Following results may be off; year out of range that algorithm has been tested with.\n");

calcEaster(year, &month, &day);

printf("Month: %i\nDay: %i\n", month, day);

return 0;
}

void calcEaster(int year, int *month, int *day)
{
// Algorithm from h2g2: http://www.bbc.co.uk/dna/h2g2/A653267
int a, b, c, d, e, f, g, h, i, j, k, m, n;

printf("Algorithm from the h2g2: http://www.bbc.co.uk/dna/h2g2/A653267\n");

a = year % 19;
b = year / 100;
c = year % 100;
d = b / 4;
e = b % 4;
f = c / 4;
g = c % 4;

h = (b + 8) / 25;
i = (b - h + 1)/ 3;
j = (19 * a + b - d - i + 15) % 30;
k = (32 + 2 * e + 2 * f - j - g) % 7;
m = (a + 11 * j + 22 * k) / 451;
n = j + k - 7 * m + 114;

*month = n / 31;
*day = (n % 31) + 1;
}