#include <iostream.h>
#include <iomanip.h>


// The following is necessary if and only if you're using an older
// compiler which doesn't recognize type "bool".  If used in combination
// with a compiler which does recognize "bool", an error will result.
// typedef enum { false = 0, true = 1 } bool;


// returns true if the year is a leap year
bool year_is_leap (int year) {

  return ((year % 4) == 0) &&
	      (((year % 100) != 0) || ((year % 400) == 0));
}


int days_in_year (int year) {

  if (year_is_leap(year)) {
    return 366;
  } else {
    return 365;
  }

}


// January = month 1, February = month 2, etc.
int days_in_month (int month, int year) {

  const int days_table [12] =
     { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

  // look after the special case
  if ((month == 2) && year_is_leap(year)) {
    return 29;
  }

  return days_table[month - 1];

}


void day_number_to_day_and_month (int day_number, int year,
                                  int &day, int &month) {

  month = 1; // start off by assuming January

  // while we've enough days left to get through another month...
  while (day_number > days_in_month (month, year)) {
    // advance to next month and reduce the number of days left to play with
    day_number -= days_in_month (month, year);
    month++;
  }

  // any days left over at this point are days into the month
  day = day_number;


}


int day_and_month_to_day_number (int day, int month, int year) {

  int day_number = 0, i;

  // add up all the days in preceding months
  for (i = 1; i < month; i++) {
    day_number += days_in_month (i, year);
  }

  // add in the number of days into the month
  day_number += day;

  return day_number;

}


int main () {

  int day, month, year, day_number, option;
  
  for (;;) {

    cout << endl
         << "Enter option" << endl
         << "  1 = day number to dd/mm" << endl
         << "  2 = dd/mm to day number" << endl
         << "  3 = quit" << endl << ": ";
    cin >> option;

    if (option == 1) {

      cout << endl << "Enter day number and year: ";
      cin >> day_number >> year;

      if ((year < 1500) || (day_number < 1) ||
          (day_number > days_in_year(year))) {
        cout << "The data entered is invalid." << endl;
      } else {
        day_number_to_day_and_month (day_number, year, day, month);
        cout << "Day: " << day << " Month: " << month << endl;
      }

    } else if (option == 2) {

      cout << endl << "Enter day, month, and year: ";
      cin >> day >> month >> year;

      if ((year < 1500) || 
          (month < 1) || (month > 12) ||
          (day < 1)||(day > days_in_month(month, year))) {
        cout << "The data entered is invalid." << endl;
      } else {
        cout << " Day number: "
             << day_and_month_to_day_number (day, month, year) << endl;
      }

    } else if (option == 3) {

      return 0; // we're all done

    } else {

      cout << endl << "Illegal option ignored." << endl;

    }

  } // end for(;;)

}