program DayOfWeek;

(* This little program calculates the day of the week from the date.
   Released to the public domain for any use whatsoever.
   William Mabee, CRNA *)

var     day, month, year,
        zday, m, y1, y2 : integer;
        NewDay          : String[4];

begin
   clrscr;
   gotoxy(1,9);
   writeln('This program computes the day of the Week from the Date');
   writeln;
   write('Enter month     : ');
   read(month);
   writeln;
   write('Enter day       : ');
   read(day);
   writeln;
   write('Enter year XXXX : ');
   read(year);
   if month < 3
   then begin
      m := month + 10;
      year := year - 1
   end else
      m := month - 2;

   y1 := year div 100;
   y2 := year mod 100;

   zday := (day + trunc(2.6 * m - 0.1)
              + y2 + y2 div 4
                   + y1 div 4 - 2*y1 + 49) mod 7;

   writeln;
   Case zday of
        0 : Newday := 'Sun';
        1 : Newday := 'Mon';
        2 : NewDay := 'Tue';
        3 : NewDay := 'Wed';
        4 : NewDay := 'Thu';
        5 : NewDay := 'Fri';
        6 : NewDay := 'Sat';
    end;

   write('Day of the week : ',Newday)
end.