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# qow 13: how to calculate easter-days for any year?

hi experts,

i am starting a new quest: qow = question of the week :-)
each week i will introduce a new simple? question.

now qow 13
(missed last later, thats why twice this week)

the first working solution will get the points (a graded).

sorry, top 15 experts, you are not allowed to solve this
q, only other can solve this question :-(

well the question is:
how to calculate easter-days for any year?

a little sample is needed

let see

meikl ;-)
0
kretzschmar
1 Solution

Commented:
Easter can only calculated from year 1 on. Before that easter is not defined.
Now tell for which calendar: Julian or Gregorian?
For the rest have a look at the Jedi Code Library. One of several ways to calculate easter sunday.
0

Commented:
I don't think it can be calculated prior to 325 A.D.
See http://www.smart.net/~mmontes/ec-cal.html for an explanation of the algorithm and restrictions.
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Commented:
Thats funny - this question was answered at the following page - www.delphiforfun.com, the source extract is below. You can get a running demo there as well.

http://www.delphiforfun.com/Programs/easter.htm

- source extract -

unit U_Easter;

{Calculates the date of Easter given any year.  I don't pretend to understand
the details of the algorithm.  It comes from the Art Of Programming series
of books by Donald Knuth}

{Gary Darby, www.dephiforfun.org}

interface

{..... generated code snipped ....}

implementation

Function KnuthCalcEaster(year:integer; var easter:TDateTime):String;
{From Vol 3 of The Art of Computer Programming, Donlad E. Knuth}
var
golden,century:integer;
Correction1,Correction2:integer;
Sunday,Epact:Integer;
N:Integer;
begin
If Year <= 1582 then
Showmessage('OK, but  results are only valid for years after 1582');
Golden := Year mod 19  + 1 ;
Century := Year div 100 + 1 ;
Correction1 := trunc(3.0 * Century / 4.0) - 12;
Correction2 := trunc((8.0 * Century + 5.0) / 25.0) - 5;
Sunday := trunc(5.0 * year / 4.0) - Correction1 -10 ;
Epact := (11 * Golden + 20 + Correction2 - Correction1) mod 30 ;
IF ((Epact = 25) and (Golden > 11))  or (Epact = 24) then
Epact := Epact + 1 ;
N := 44 - Epact;
if N < 21 then  N := N + 30 ;
N := N + 7 - ((Sunday + N) mod 7) ;
try
{Pass a Year, Month, and Day and get a date back}
easter:=encodedate(year,3,1)+n-1;
result:=FormatDateTime('mmmm d',easter);
except
showmessage(inttostr(year)+' is an invalid year');
result:='';
easter:=0;
end;
end;

Procedure TForm1.getdate(Year:integer);
{take a year, calculate Easter date and display it}
var
iswas:string;
s:string;
Easter:TDateTime;
begin
s:=Knuthcalceaster(year,Easter);
If easter>now then iswas:=' will be on '
else iswas:=' was on ';
Easter2lbl.Caption:='Easter in '+inttostr(year)
+ iswas +s;
Intedit1.text:=inttostr(year);
end;

procedure TForm1.IntEdit1KeyPress(Sender: TObject; var Key: Char);
{Get integers and show Easter when Enter key is pressed}
begin
If key=#13 then
begin
Getdate(strtoint(IntEdit1.text));
key:=#00;
end
else if not (key in ['0'..'9']) then
begin  beep;  key:=#00; end;
end;

procedure TForm1.FormActivate(Sender: TObject);
var
y,m,d:word;
m2,d2:integer;
e1,e2:TDateTime;
s1,s2:string;
begin
{set current data at start up time}
decodedate(now,y,m,d);
getdate(y);
end;

procedure TForm1.IntEdit1Click(Sender: TObject);
begin {also show Easter if year is clicked}
getdate(strtoint(intedit1.text));
end;

end.
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Author Commented:
yep, works perfect

thanks for participating on this quest

next monday the next ?simple q

meikl ;-)
0
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