#include <string>
#include <iostream>

using namespace std;  

/* want to be able to say, for example:
     date today(2023, 2, 2);
     today.print();
     today.increment();
     today.print();
     today.set(1987, 12, 31);
     today.increment();
     today.print(); */

class date
{ protected:  // only methods of this class can access these variables
    int day, month, year, dow;

  public:
    date(int y, int m, int d);
    void set(int y, int m, int dy);
    void print();
    void increment(); };

string mname[] = { "", "January", "February", "March", "April",
                   "May", "June", "July", "August", 
                   "September", "October", "November", "Decemeber" };

string dname[] = { "Sunday", "Monday", "Tuesday", "Wednesday",
                   "Thursday", "Friday", "Saturday" };

string stndrdth(int n)
{ if (n == 1 || n == 21 || n == 31)
    return "st";
  if (n == 2 || n == 22)
    return "nd";
  if (n == 3 || n == 23)
    return "rd";
  return "th"; }

bool is_leap_year(int y)
{ if (y % 400 == 0) return true;
  if (y % 100 == 0) return false;
  if (y % 4 == 0) return true;
  return false; }

int days_in(int y, int m)
{ if (m == 4 || m == 6 || m == 9 || m == 11)
    return 30;
  if (m != 2)
    return 31;
  if (is_leap_year(y))
    return 29;
  return 28; }
    
int day_number(int y, int m, int d)
{ int t = y * 365;
  t += (y + 3) / 4;
  t -= (y + 99) / 100;
  t += (y + 399) / 400;
  for (int i = 1; i < m; i += 1)     
    t += days_in(y, i);
  t += d;
  return t; }

date::date(int y, int m, int d)
{ set(y, m, d); }

void date::set(int y, int m, int dy)
{ year = y;
  month = m;
  day = dy;
  int d = day_number(year, month, day);
  dow = (d + 5) % 7; }

void date::print()
{ cout << dname[dow] << " " << day << stndrdth(day) << " " << mname[month] << " " << year << "\n"; }

void date::increment()
{ dow = (dow + 1) % 7;
  day += 1;
  if (day > days_in(year, month))
  { day = 1;
    month += 1; 
    if (month == 13)
    { month = 1;
      year += 1; } } }

int main()
{ cout << "2nd February 2023 is day number " << day_number(2023, 2, 2) << " A.D.\n";
  date today(2023, 2, 2);
  today.print();
  today.increment();
  today.print();
  today.set(1987, 12, 31);
  today.increment();
  today.print();
}