Дана дата в формате день:месяц:год. Определить дату через n дней

#include <iostream>
 
bool IsLeapYear(int y)
{
    return (y%4 == 0 && y%100 != 0) || (y%400 == 0);
}
 
int DaysInMonth(int month, int year)
{
    static const int daysInMonth[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
 
    if (month == 2 && IsLeapYear(year))
        return 29;
 
    return daysInMonth[month-1];
}
 
void AdvanceDate(int nDays, int &d, int &m, int &y)
{
    int dm = DaysInMonth(m, y);
 
    if (dm-d >= nDays) {
        d += nDays;
        return;
    }
    else {
        nDays -= (dm-d+1);
        d = 1;
        ++m;
    }
 
    while (true)
    {
        int dm = DaysInMonth(m, y);
 
        if (dm-d >= nDays) {
            d += nDays;
            break;
        }
        else
            nDays -= (dm - d + 1);
 
        if (++m > 12) {
            m = 1;
            ++y;
        }
    }
}
 
int main()
{
    int day = 18, month = 4, year = 2017;
    int nDays = 4*365;
 
    AdvanceDate(nDays, day, month, year);
 
    std::cout << day << " " << month << " " << year << "\n";
}

void main()
{
    int Day = 0;
    cout << "Day: ";
    cin >> Day;
    cout << "Month: ";
    int Month = 0;
    cin >> Month;
    cout << "Year: ";
    int Year = 0;
    cin >> Year;
    cout << "Enter N: ";
    int N_Days = 0;
    cin >> N_Days;
    
    AdvanceDate(N_Days, Day, Month, Year);
 
    cout << "After " << N_Days << " days date will be:" << Day << " " << Month << " " << Year << "\n";
    
    system("pause");
}

#include<iostream>
 
using namespace std;
 
struct DATE
{
    int Day;
    int Month;
    int Year;
};
 
int CheckIsLeapYear(int y)//Checks that year is a leap or not
{
    if (y % 400 == 0) return 1;
    if (y % 100 == 0) return 0;
    if (y % 4 == 0) return 1;
    return 0;
}
int DaysInMonth(int month, int year)//Checks how many days in the month
{
    static const int NumberOfDays[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
 
    if (month == 2 && CheckIsLeapYear(year))
        return 29;
 
    return NumberOfDays[month - 1];
}
void AdvanceDate(int N_Days, int &day, int &m, int &y)//Calculates the date after a few days
{
    int dayofmonth = DaysInMonth(m, y);
 
    if (dayofmonth - day >= N_Days) {
        day += N_Days;
        return;
    }
    else {
        N_Days -= (dayofmonth - day + 1);
        day = 1;
        ++m;
    }
    while (true)
    {
        int dayofmonth = DaysInMonth(m, y);
 
        if (dayofmonth - day >= N_Days) {
            day += N_Days;
            break;
        }
        else
            N_Days -= (dayofmonth - day + 1);
 
        if (++m > 12) {
            m = 1;
            ++y;
        }
    }
}
void main()
{
    DATE DMY;
    int Day = 0;
    cout << "Day: ";
    cin >> DMY.Day;
    cout << "Month: ";
    int Month = 0;
    cin >> DMY.Month;
    cout << "Year: ";
    int Year = 0;
    cin >> DMY.Year;
    cout << "*** ANALYZING ENTERED THE DATE, SET THE DATE ON N DAYS AHEAD ***" << "\n";
    //Enter count of days
    cout << "Enter N_Days: ";
    int N_Days = 0;
    cin >> N_Days;
    //Calculates the date wich will be after entered count of dats
    AdvanceDate(N_Days, DMY.Day, DMY.Month, DMY.Year);
    cout << "After " << N_Days << " days date will be:" << DMY.Day << " " << DMY.Month << " " << DMY.Year << "\n\n";
 
    system("pause");
}