#include <iostream>
#include <cstdlib>
#include <chrono>   //for class system_clock
#include <ctime>    //for the function localtime
using namespace std;

void travel(int& hour, int& mins, int& sec, int distance);

int main()
{
	const auto now {chrono::system_clock::now()};
	const time_t t {chrono::system_clock::to_time_t(now)};
        const tm *const p {localtime(&t)};

	//Get the current year, month, and day of the month.
	int h {p->tm_hour};
	int m {p->tm_min};   //in the range 1 to 12 inclusive
	int s {p->tm_sec};      //in the range 1 to 31 inclusive

	cout << "How many seconds forward do you want to go from "
		<< h << ":" << m << ":" << s << "? ";
	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;
	}

	//The following statement can change the value of m, d, y,
	//but not the value of distance.
	travel(m, s, h, distance);

	cout << "The new time is: "
		<< h << ":" << m << ":" << s << "\n";

	return EXIT_SUCCESS;
}

//Move the date distance days into the future.

void travel(int& mins, int& sec, int& hour, int distance)
{

	/*
	Walk distance days into the future.
	Each iteration of the loop advances 1 day into the future.
	Each ++day, ++month, ++year will now change the value of an actual
	argument up in main.
	*/

	for (int i {0}; i < distance; ++i) {
		++sec;
		if (sec >= 60) {
			sec = 0;
		       ++mins;	
		} if (mins >= 60){
			mins = 0;
	   		++hour;		//Advance into a new month.
			 
			}
		}
	}