easter.pas

program Easter (input, output) ;
Uses sysutils;

procedure showHelp;
begin
   writeln('Easter');
   writeln;
   writeln('Usage:');
   writeln(#9'easter [-c][-h] [CCYY]');
   writeln;
   writeln('Will output the date of Easter for a given year.');
   writeln;
   writeln('-c'#9'Formats the output for use in calendar.');
   writeln('-h'#9'Outputs this help message.');
   writeln;
   writeln('CCYY should be the four digit year.');
   writeln;
   writeln('Michael J Chappell  15 April 2024');
   writeln('mcsuper5@freeshell.org');
end;

procedure calendarOutput(date , year : integer; april : boolean);
begin
   if april then write ('4/') else write ('3/');
   writeln (date,#9'Easter (',year,')');   
end;

procedure humanOutput(date , year : integer; april : boolean);
begin
   write ('Easter is on ');
   if april then write ('April') else write ('March');
   writeln (' ',date,', ',year);   
end;

var
   a, b, c, d, e : integer;
   i		 : integer;
   code		 : integer;
   date		 : integer;
   year		 : integer;
   april	 : boolean;
   calendar	 : boolean;
   help		 : boolean;
   numset	 : boolean;

Begin
   numset   := False;
   calendar := False;
   help     := False;
   for i := 1 to ParamCount do
      begin
	 if ansiCompareStr(ParamStr (i),'-h')=0 then help := True;
	 if ansiCompareStr(ParamStr (i),'-c')=0 then calendar := True;
	 (* Val sets second argument to value and third to position of 
	  the first invalid character *)
	 Val(ParamStr (i), year, code);
	 if code = 0 then numset := True;
      end;

   if NOT help then
      begin
	 (* Get Year *)
	 if (ParamCount = 0) or NOT numset  then
	 Begin
	    Write('Enter year>  ');
	    Readln(year);
	 End; 

	 (* Find the date in March.  I don't recall where I found this 
	    algorithm. 
	  *)
	 a := year mod 19;
	 b := year mod 4;
	 c := year mod 7;
	 d := (19*a+24) mod 30;
	 e := (2*b+4*c+6*d+5) mod 7;
	 date := 22+d+e;

	 (* Fix the date if it falls in April and set flag *)
	 if (date > 31) then
	    begin
	       april := true;
	       date := date mod 31;
	    end
         else
            begin
	       april := false;
            end
      end;
   (* Output *)
   if help then
      begin
	 showHelp
      end
   else if calendar then
      begin
	 calendarOutput(date, year, april);
      end
   else
      begin
	 humanOutput(date, year, april);
      end;
End.
This source has been viewed 13 times.
Saturday, 13 December 2025 Michael J. Chappell Contact me at: mcsuper5@freeshell.org
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