#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

class date {
	int year;
	int month; 
	int day;  

	static const int length[13];  

public:
	date(int m, int d, int y); 
	date();  

	void print() const;
	void next(int n);
	void next();
	int dayOfYear() const; 

	friend int distance(const date& d1, const date& d2);
};

int main() {
	try {
		const date independenceDay {7, 4, 1776};  
		independenceDay.print();
		cout << " is Independence Day.\n";

		const date t;
		cout << "Today is ";
		t.print();
		cout << ".\n";

		const time_t now {time(nullptr)};
		const tm *const p {localtime(&now)};
		const date today {p->tm_mon + 1, p->tm_mday, p->tm_year + 1900};
		today.print();
		cout << " is today.\n";

		const date xmas {12, 25, 2025};
		cout << "Christmas is day number " << xmas.dayOfYear() << " of the year.\n";

		const date summer {6, 20, 2025};  
		const int dist {distance(summer, t)};
		cout << "Only " << dist << " days till summer.\n";
	}
	catch (invalid_argument& e) {
		cerr << e.what() << "\n";
		return EXIT_FAILURE;
	}

	return EXIT_SUCCESS;
}

const int date::length[] = {
	 0,   
	31, 
	28, 
	31,
	30, 
	31, 
	30,
	31, 
	31, 
	30, 
	31, 
	30, 
	31  
};

date::date(int m, int d, int y) {
	year = y;
	if (m < 1 || m > 12) throw invalid_argument("bad month");
	month = m;

	if (d < 1 || d > length[month]) throw invalid_argument("bad day of the month");
	day = d;
}

date::date() {
	const time_t now = time(nullptr);
	const tm *const p = localtime(&now);
	month = p->tm_mon + 1;
	day = p->tm_mday;
	year = p->tm_year + 1900;
}

void date::print() const {
	cout << month << "/" << day << "/" << year;
}

void date::next(int n) {
	for (int i = 0; i < n; ++i) {
		next();
	}
}

void date::next() {
	if (day < length[month]) {
		++day;
	} else {
		day = 1;
		if (month < 12) {
			++month;
		} else {
			month = 1;
			++year;
		}
	}
}

int date::dayOfYear() const {
	int sum = day;
	for (int i = 1; i < month; ++i) {
		sum += length[i];
	}
	return sum;
}

int distance(const date& d1, const date& d2) {
	const int days1 = d1.dayOfYear() + (d1.year * 365);
	const int days2 = d2.dayOfYear() + (d2.year * 365);
	return days1 - days2;
}