🚀 go-pugleaf

Hi,

on January 24, 1996 you wrote:

> Hi, can anybody send me a C function to calculate the Easter of every 
> year? Thanks in advance,
>                         Andrea.

Then this guy came up with a Gauss algorithm put into a Pascal (yagh!) 
procedure:

Abe Timmerman
Hogeschool Holland
(HHIT: Center for education and Information Technology)
The Netherlands
Email:A.Timmerman@Beta.hsholland.nl

Next ofcourse somebody asked for the C version, which you did in the 
first place. 

Below you will find the Pascal procedure converted to a C function
and a (tested) sample program that calls the function. This is by far
not the most elegant C function I have ever seen, but it is meant 
to follow the Pascal procedure step by step. I do not know if limits
for the year exist and if so what they are (besides ofcourse the obvious
ones), I did not test for any:

=========================================================================
#include    <stdio.h>

void    Easter(int * Month, int * Day, int Year);

void    main()
{
    int y, m, d;

    for (y = 1800; y <= 2000; y++) {
        Easter(&m, &d, y);             
        printf("Year: %4d, Month: %2d, Day: %2d\n", y, m, d);
    }

}


/*
    C version for the Gauss-Easter algorithm

    Based on the formulas/algorithm published bij Gauss in 1800

    Input:            - pointers to ints Month and Day
                      - int Year where 1800 <= Year <= 2000 (?)

    Input-validation: none (sensible input assumed for Year)

*/
void    Easter(int * Month, int * Day, int Year)
{
    int a, b, c, d, e, f, k, m, n, p, q;

    a = Year % 19;
    b = Year % 4;
    c = Year % 7;
    k = Year / 100;
    p = k / 3;
    q = k - k / 4;
    m = (q - p + 15) % 30;
    n = (q + 4) % 7;
    d = (19 * a + m) % 30;
    e = (2 * b + 4 * c + 6 * d + n) % 7;
    f = d + e - 9;
    if  (f <= 0) {
        *Month = 3;
        *Day = 31 + f;
    }
    else {
        *Month = 4;
        if   (f == 26)
            *Day = 19;
        else if (f == 25 && d == 28)
            *Day = 18;
        else
            *Day = f;
    }
}
=========================================================================

Hope this helps,

Piet Starreveld
e-mail:101476.1040@compuserve.com