#chrono.h
=======================================================================================================================================
#pragma once
#include <iostream>


namespace chrono {
	enum class Month {
		jan = 1, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec
	};

	class Date {
	public:
		class Invalid {
			Invalid() = default;
		};
		Date(int y, Month m, int d);

		Date();

		int day() const { return d; }
		Month month() const { return m; }
		int year() const { return y; }
		void add_day(int n);
		void add_month(int n);
		void add_year(int n);

	private:
		int y;
		Month m;
		int d;

	};

	bool is_date(int y, Month m, int d);
	bool leapyear(int y);
	bool operator==(const Date& a, const Date& b);
	bool operator!=(const Date& a, const Date& b);
	std::ostream& operator<<(std::ostream& os, const Date& d);
	std::istream& operator>>(std::istream& is, Date& dd);

}
=======================================================================================================================================
#chrono.cpp
=======================================================================================================================================
#include "chrono.h"

namespace chrono {
	Date::Date(int yy, Month mm, int dd) : y(yy), m(mm), d(dd) {
		if (!is_date(yy, mm, dd)) throw Invalid{};
	}

	const Date& default_date() {
		static Date dd{ 2001, Month::jan, 1 };
		return dd;
	}

	Date::Date() : y{ default_date().year() }, m(default_date().month()), d{ default_date().day() } {

	}

	void Date::add_day(int n) {
		d+=n;
	}

	void Date::add_month(int n) {

	}

	void Date::add_year(int n) {
		if (m == Month::feb && d == 29 && !leapyear(y + n)) {
			m = Month::mar;
			d = 1;
		}
		y += n;
	}

	bool is_date(int y, Month m, int d) {
		if (d <= 0) 
			return false;
		if (m < Month::jan || Month::dec < m) return false;

		int days_in_month = 31;
		switch (m) {
		case Month::feb:
			days_in_month = (leapyear(y)) ? 29 : 28;
			break;

		case Month::apr: case Month::jun: case Month::sep: case Month::nov:
			days_in_month = 30;
			break;
		}

		if (days_in_month < d) return false;
		return true;
	}

	bool leapyear(int y) {
		if((y % 4 == 0 && y % 100 != 0) || y % 400 == 0) {
			return true;
		}
		else {
			return false;
		}
	}

	bool operator==(const Date& a, const Date& b) {
		return a.year() == b.year()
			&& a.month() == b.month()
			&& a.day() == b.day();
	}

	bool operator!=(const Date& a, const Date& b) {
		return !(a == b);
	}

	std::ostream& operator<<(std::ostream& os, const Date& d){
		return os << '(' << d.year()
			<< ", " << static_cast<int>(d.month())
			<< ", " << d.day() << ')';
	}

	std::istream& operator>>(std::istream& is, Date& dd){
		int y, m, d;
		char ch1, ch2, ch3, ch4;
		is >> ch1 >> y >> ch2 >> m >> ch3 >> d >> ch4;
		if (!is) return is;
		if (ch1 != '(' || ch2 != ',' || ch3 != ',' || ch4 != ')') {
			is.clear(std::ios_base::failbit);
			return is;
		}
		dd = Date(y, Month(m), d);
		return is;
	}

	enum class Day {
		sunday, monday, tuesday, wednesday, thursday, friday, saturday
	};
	
	/*void day_of_week(const Date& d) {

	}

	void next_Sunday(const Date& d) {

	}

	void next_weekday(const Date& d) {

	}*/
} //chrono
=======================================================================================================================================
#main.cpp
=======================================================================================================================================
#include <iostream>
#include "chrono.h"

int main() {
	chrono::Date today{ 1963, chrono::Month::may, 32 };
	chrono::Date tomorrow = today;
	tomorrow.add_day(1);

	std::cout << today << " " << tomorrow;
}