%-------------------------------------%
% Homework 5: 4.17                    %
% Date: 10/21/2002                    %
%                                     %
% Gun Srijuntongsiri                  %
% gs61                                %
% ??????                              %
%-------------------------------------%

% Variables:
%   day         --  Day (dd) 
%   day_of_year --  Day of year
%   ii          --  Loop index
%   month       --  Month (mm)
%   year        --  Year (yyyy)
%   valid       --  whether it's a valid day/month/year

% Get day, month, and year to convert
disp('This program calculates the day of year give the ');
disp('current date.');
month = input('Enter current month (1-12): ');
day   = input('Enter current day (1-31):   ');
year  = input('Enter current year(yyyy):   ');

% Check for leap year, and add extra day if necessary
if mod(year,400) == 0
    leap_day = 1;
elseif mod(year,100) == 0
    leap_day = 0;
elseif mod(year,4) == 0
    leap_day = 1;
else
    leap_day = 0;
end

% Check for legal day, month, and year
valid = 1;    % assume valid input first

% If year <= 0, month not in 1 to 12, day < 1, it's invalid
if (year <= 0)
    disp('Year is invalid');
    valid = 0;
elseif (month <1) | (month > 12)
    disp('Month is invalid');
    valid = 0;
elseif (day < 1)
    disp('Day is invalid');
    valid = 0;
else       % if still valid, check that day not larger than
           %   maximum number of days on that month
    switch(month)
        case {1,3,5,7,8,10,12},
            if day > 31, valid = 0; end
        case {4,6,9,11},
            if day > 30, valid = 0; end
        case 2
            if day > 28+leap_day, valid=0; end
    end

    if valid==0, disp('Day is invalid'); end
end

if valid~=0

    % Calculate day of year by adding current day to the days
    % in previous months.
    day_of_year = day;
    for ii= 1:month-1
    
        % Add days in months from January to last month
        switch(ii)
            case {1,3,5,7,8,10,12},
                day_of_year = day_of_year + 31;
            case {4,6,9,11},
                day_of_year = day_of_year + 30;
            case 2,
                day_of_year = day_of_year + 28 + leap_day;
         end
    
    end

    % Tell user
    fprintf('The date %2d/%2d/%4d is day of year %d.\n', ...
        month, day, year, day_of_year);

end