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

class date {
public:
	//Data members:
	int year;
	int month;  //in the range 1 to 12 inclusive
	int day;    //in the range 1 to 31 inclusive

	//Member functions:
	void print() const; //const member function
	void next(int n);   //non-const member function
	void next();
	void prev(int n); //Go n days into the past.
	void prev();      //Go 1 day into the past.
};

int main()
{

	// take March 1, 2025 back one day with prev() function
	date march_1_2025 {2025, 3, 1};
	date feb_28_2025 {march_1_2025};
	feb_28_2025.prev();
	feb_28_2025.print();
	cout << " is one day before March 1, 2025." << endl;

	// Take March 1, 2025 back n days with prev(int n) function
	int n;
	while (true) {
		cout << "How many days before March 1, 2025 should we travel?  Please enter an integer: ";

		cin >> n;
		if (cin.fail()) { // Check if input is valid
			cin.clear(); // Clear the error flag
			cin.ignore(numeric_limits<streamsize>::max(), '\n'); // Ignore invalid input
			cerr << "Invalid input.  Please enter an integer." << endl;
		}
		else 
			break; // Input is valid; break the loop
	}

	date march_1_2025_prev {march_1_2025};
	march_1_2025_prev.prev(n);
	march_1_2025_prev.print();
	cout << " is " << n << " days before March 1, 2025." << endl;


	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
};

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 < date_length[month]) {
		++day;
	} else {
		day = 1;             //Advance into the next month.
		if (month < 12) {
			++month;
		} else {
			month = 1;   //Advance into the next year.
			year++;
		}
	}
}

void date::prev(int n) { // Move this date n days into the past
	for (int i = 0; i < n; i++) {
		prev(); // call prev() function with no argument n times
	}

}

void date::prev() { // Move this date one day into the past
	if (day > 1)
		day--;
	else {
		if (month > 1) {
			month--; // update month
			day = date_length[month]; // update day
		}
		else { // month == 1
			year--; // update year
			month = 12; // update month
			day = date_length[month]; // update day
		}
	}
}