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

struct date {
	int year;
	int month;  //in the range 1 to 12 inclusive
	int day;    //in the range 1 to 31 inclusive
};

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
};

//Function declarations.
void print(const date *p);
void next(date *p, int n);
void next(date *p);

int main()
{
	const date independenceDay {1776, 7, 4};
	print(&independenceDay);
	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_year + 1900, p->tm_mon + 1, p->tm_mday};
	print(&today);
	cout << " is today.\n";

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

	//Output the date of next Christmas, 329 days from today (Jan 30 2025).
	date christmas {today};
	next(&christmas, 329);
	print(&christmas);
	cout << " is next Christmas.\n";

	return EXIT_SUCCESS;
}

void print(const date *p)   //Can't change the date struct.
{
	cout << p->month << "/" << p->day << "/" << p->year;
}

void next(date *p, int n)   //Can change the date struct.
{
	for (int i {0}; i < n; ++i) {
		next(p); //Call the other next function, the one with 1 argument
	}
}

void next(date *p)   //Move this date one day into the future.
{
	if (p->day < date_length[p->month]) {
		++p->day;             //increments p->day, not p
	} else {
		p->day = 1;           //Advance into the next month.
		if (p->month < 12) {
			++p->month;
		} else {
			p->month = 1; //Advance into the next year.
			++p->year;
		}
	}
}