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Introduction

Looking through old Pascal sources I found an algorithm to calculate Easter Sunday. I reinterpreted it to C++ and packed it into a small MFC dialog application.

The sample calculates Easter from 1970 to 2037. Responsible for the limitation is the function mktime, used to calculate the offset to ash. Basically GetEasterSunday is able to calculate Easter from 1583 (beginning of Gregorian calendar) to 2499 (end of correction values).

Ash Wednesday is 46 days before Easter Sunday.

void
CEasterDlg::GetEasterSunday( WORD wYear, WORD& wMonth, WORD& wDay )
{
    // calculate easter sunday

    // [in]  wYear  - 4-digit year to calculate (but not before 1583)

    // [out] wMonth - month of easter sunday

    // [out] wDay   - day of easter sunday


    WORD wCorrection = 0;   
    
    if( wYear < 1700 )      wCorrection = 4;
    else if( wYear < 1800 ) wCorrection = 5;
    else if( wYear < 1900 ) wCorrection = 6;
    else if( wYear < 2100 ) wCorrection = 0;
    else if( wYear < 2200 ) wCorrection = 1;
    else if( wYear < 2300 ) wCorrection = 2;
    else if( wYear < 2500 ) wCorrection = 3;

    wDay = (19 * (wYear % 19) + 24) % 30;        
    wDay = 22 + wDay + ((2 * (wYear % 4) + 4 * (wYear % 7) + 6 * wDay + 5 + wCorrection) % 7);
    
    // jump to next month

    if( wDay > 31 )
    {
        wMonth = 4;
        wDay -= 31;
    }
    else
    {
        wMonth = 3;
    }
}

Further reading:

Have fun.

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The algorithm is incorrect Sire404 5:42 22 Mar '05   It gives the wrong date for a handful of years between 1583 and 2005, for example 1981. Try this alrorithm[^] (c++) instead. -------------------- No one is perfect. Welll, there was this guy... but we killed him. Sign In·View Thread·PermaLink 2.00/5 There are better algorithms. Willzyba 4:22 22 Nov '04   Try: http://www.codecogs.com/d-ox/group__easter_sunday.html Code will be available (for free!) soon. Will http://www.codecogs.com Sign In·View Thread·PermaLink It does not take into account all the Christians Alexandru Savescu 13:39 27 Nov '01   This is a very useful calendar problem, maybe you could explain the formulas as well. However, a large part of the Christians are of orthodox religion (Eastern Europe, Russia, etc.) and will not find your program useful. As far as I know, most of the time the orthodox religion has Easter Sunday a week after the Catholics, but sometimes (once every pope knows how many years) Easter Sunday is the same day for all Christians. Maybe you can adjust your program. Sign In·View Thread·PermaLink Just what I was looking for! Matt Gullett 10:09 26 Nov '01   Thanks! Sign In·View Thread·PermaLink Dead link? edx 7:30 26 Nov '01   http://aa.usno.navy.mil/data/docs/easter.html this linkt seems to be dead... is it down or just a misspelling? [edx] Sign In·View Thread·PermaLink heheh Rui Lopes 1:56 25 Nov '01   This is great for making calendar software! Btw.. why not add some more algorithms? Moon fases for example... ---- Rui Lopes Sign In·View Thread·PermaLink unusual :-) Nish [BusterBoy] 21:09 24 Nov '01   The article is on an unusual topic. But cheers, cause it adds to the CP variety Nish Sonork ID 100.9786 voidmain www.busterboy.org Nish is a BIG fan of Goran Ivanisevic Sign In·View Thread·PermaLink

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