#include <iostream>
#include <cstdlib>
#include <ctime>    //for the functions time and localtime
using namespace std;

class date {
	//Declarations for data members:
	int year;
	int month;  //in the range 1 to 12 inclusive
	int day;    //in the range 1 to 31 inclusive

	static const int length[13];        //static data member (needs the 13)

public:                                     //private by default
	//Declarations for member functions:
	date(int m, int d, int y);          //constructor
	int dayOfYear() const;
	friend int distance(const date& d1, const date& d2);
	void print() const;                 //const member function
	void next(int n);                   //non-const member function
	void next();
};

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

		//Ask the operating system for the current date and time.
		const time_t t {time(nullptr)};
		const tm *const p {localtime(&t)};

		//Output today's date.
		const date today {p->tm_mon + 1, p->tm_mday, p->tm_year + 1900};
		today.print();
		cout << " is today.\n";

		//Output tomorrow's date.
		date tomorrow {today};
		tomorrow.next();   //Advance one day.
		tomorrow.print();
		cout << " is tomorrow.\n";

		//Output the date of next Christmas, 321 days from today (Feb 6 2025).
		date christmas {today};
		christmas.next(321);
		christmas.print();
		cout << " is next Christmas.\n";

		const date summer {6, 20, 2025};
		const date t;
		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,   //dummy, so that January will have subscript 1
	31,   //January
	28,   //February.  Pretend there are no leap years.
	31,   //March
	30,   //April
	31,   //May
	30,   //June
	31,   //July
	31,   //August
	30,   //September
	31,   //October
	30,   //November
	31    //December
};

//The constructor installs 3 valid values into a newborn date object,
//or it throws an exception.

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;
}

void date::print() const  //Can't change the date object.
{
	cout << month << "/" << day << "/" << year;
}

void date::next(int n)   //Can change the date object.
{
	for (int i {0}; i < n; ++i) {
		next(); //Call the other next function, the one with no argument
	}
}

void date::next()   //Move this date one day into the future.
{
	if (day < length[month]) {
		++day;
	} else {
		day = 1;             //Advance into the next month.
		if (month < 12) {
			++month;
		} else {
			month = 1;   //Advance into the next year.
			++year;
		}
	}
}