#include <iostream>
#include <cstdlib>
#include <ctime>   //for time_t, time, tm, localtime
using namespace std;

int main()
{
	int length[][13] {
	      //dum Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
		{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, //non-leap
		{0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}  //leap
	};

	int n {12};   //number of months in a year

	//Get the current year, month, and day of the month.
	time_t t {time(nullptr)};
	tm *p {localtime(&t)};

	int year {p->tm_year + 1900};
	int month {p->tm_mon + 1};   //in the range 1 to 12 inclusive
	int day {p->tm_mday};        //in the range 1 to 31 inclusive

	cout << "How many days forward do you want to go from "
		<< month << "/" << day << "/" << year << "? ";
	int distance {0};
	cin >> distance;

	if (!cin) {
		cerr << "Sorry, that wasn't a number.\n";
		return EXIT_FAILURE;
	}

	if (distance < 0) {
		cerr << "Distance " << distance << " can't be negative.\n";
		return EXIT_FAILURE;
	}

	//Walk distance days into the future.
	//Each iteration of the loop advances 1 day into the future.

	for (int i {0}; i < distance; ++i) {
		int leap {0};     //will be used as a subscript
		if (year % 400 == 0 || year % 100 != 0 && year % 4 == 0) {
			leap = 1; //year is a leap year
		} else {
			leap = 0; //year is not a leap year
		}

		if (day < length[leap][month]) {
			++day;
		} else {
			day = 1;            //Advance into a new month.
			if (month < n) {
				++month;
			} else {
				month = 1;  //Advance into a new year.
				++year;
			}
		}
	}

	cout << "The new date is "
		<< month << "/" << day << "/" << year << ".\n";

	return EXIT_SUCCESS;
}