{
    This program asks the user for a year, and prints a calendar for that year.
}
program calendar (input, output);

const
    JAN = 1;
    FEB = 2;
    MAR = 3;
    APR = 4;
    MAY = 5;
    JUN = 6;
    JUL = 7;
    AUG = 8;
    SEP = 9;
    OCT = 10;
    NOV = 11;
    DEC = 12;
    BLANK = ' ';

var
    month, year, dayFor1st : integer;

{
    Get the year from the user, and compute (using a magic formula) the day
    on which its January 1 falls.  Sunday is 0, Monday 1, etc.  The formula
    to find the first day of the given year was found in the book "A Collection
    of Programming Problems and Techniques", by H.A. Maurer and M.R. Williams
    (Prentice-Hall, 1972).
}
procedure GetYearInfo (var year, dayFor1st : integer);
var
    y : integer;

    {
	We will only deal with years AD.
    }
    function Legal (year : integer) : boolean;
    begin
	Legal := (year > 0);
    end;

    begin {GetYearInfo}
	repeat
	    write ('Please type the year you want a calendar for: ');
	    readln (year);
	    if not Legal (year) then begin
		writeln ('Can''t make a calendar for that year.');
	    end;
	until Legal (year);
	y := year - 1;
	dayFor1st := (36 + y + y div 4 - y div 100 + y div 400) mod 7;
    end   {GetYearInfo};

#include "numdays.i";
#include "wkbywk.i";

begin {main program}
    GetYearInfo (year, dayFor1st);
    for month := JAN to DEC do begin
	PrintMonth (month, year, dayFor1st);
	dayFor1st := (dayFor1st+NumberOfDaysIn(month, year)) mod 7;
    end;
end   {main program}.