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

int main()
{
	int length[] {
		 0,   //dummy element so that January will have subscript 1
		31,   //January
		28,   //February
		31,   //March
		30,   //April
		31,   //May
		30,   //June
		31,   //July
		31,   //August
		30,   //September
		31,   //October
		30,   //November
		31    //December
	};

	int n {size(length) - 1}; //the number of months, not counting the dummy

	//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) {
		if (day < length[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;
}