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

class date {
	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:
	date(int month, int day, int year); //constructor
	void print() const;                 //const member function
	void next(int n);                   //non-const member function
	void next();
};

int main()
{
	const date independenceDay {7, 4, 1776};
	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, 329 days from today (Jan 30 2025).
	date christmas {today};
	christmas.next(329);
	christmas.print();
	cout << " is next Christmas.\n";

	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.
//this is a pointer to the object being constructed, so
//this->year is a data member belonging to the object being constructed.
//Plain old year without the this-> is an argument of the constructor.

date::date(int month, int day, int year)
{
	this->year = year;
	if (month < 1 || month > 12) {
		throw invalid_argument("bad month");
	}
	this->month = month;
	if (day < 1 || day > length[month]) {
		throw invalid_argument("bad day of the month");
	}
	this->day = day;
}

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

void date::next(int n)   //Can change the date struct.
{
	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;
		}
	}
}