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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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