#include <iostream>
using namespace std;
int newdays;
struct time
{
    long year;
    int month;
    int day;
    time()
    {
        year = 0;
        month = 0;
        day = 0;
    }
};


int newday()
{
    cout << "Введите количество дней " << endl;
    cin >> newdays;
    return newdays;
}
void positive(time first, int result_newday)
{
            while (result_newday--) {
                first.day++;
                switch (first.month) {
                case 1:
                case 3:
                case 5:
                case 7:
                case 8:
                case 10:
                case 12: {
                    if (first.day > 31) {
                        first.month++;
                        first.day -= 31;
                    }
                    break;
                }

                case 2: {
                    if (first.year % 4 == 0) {
                        if (first.year % 100 == 0) {
                            if (first.year % 400 == 0) {
                                if (first.day > 29) {
                                    first.month++;
                                    first.day -= 29;
                                }
                            }
                            else if (first.day > 28) {
                                first.month++;
                                first.day -= 28;
                            }
                        }
                        else if (first.day > 29) {
                            first.month++;
                            first.day -= 29;
                        }
                    }
                    else if (first.day > 28) {
                        first.month++;
                        first.day -= 28;
                    }
                    break;
                }
                case 4:
                case 6:
                case 9:
                case 11: {
                    if (first.day > 30) {
                        first.month++;
                        first.day -= 30;
                    }
                    break;
                }
                default:
                    break;
                }

                while (first.month > 12) {
                    first.month -= 12;
                    first.year++;
                }
            }
            cout << "Новая дата: " << first.day << '.' << first.month << '.' << first.year << endl;
        }

int negative(time first, int result_newday) {

    while (result_newday++) {
        first.day--;
        switch (first.month) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12: {
            if (first.day < 31) {
                first.month--;
                first.day += 31;
            }
            break;
        }

        case 2: {
            if (first.year % 4 == 0) {
                if (first.year % 100 == 0) {
                    if (first.year % 400 == 0) {
                        if (first.day < 29) {
                            first.month--;
                            first.day += 29;
                        }
                    }
                    else if (first.day < 28) {
                        first.month--;
                        first.day += 28;
                    }
                }
                else if (first.day < 29) {
                    first.month--;
                    first.day += 29;
                }
            }
            else if (first.day < 28) {
                first.month--;
                first.day += 28;
            }
            break;
        }
        case 4:
        case 6:
        case 9:
        case 11: {
            if (first.day < 30) {
                first.month--;
                first.day += 30;
            }
            break;
        }
        default:
            break;
        }

        while (first.month < 1) {
            first.month += 12;
            first.year--;
        }
        if (first.year < 0) {
            cout << "Калькулятор работает только в пределах нашей эры!" << endl;
            return 0;
        }
        cout << "Новая дата: " << first.day << '.' << first.month << '.' << first.year << endl;
    }
    return 0;
}

void calculator(time first) {
    cout << "Введите изначальную дату(день, месяц, год): " << endl;
    cin >> first.day;
    cin >> first.month;
    cin >> first.year;
    cout << "Изначальная дата: " << first.day << "." << first.month << "." << first.year << endl;
    int result_newday = newday();
    if (result_newday>0)
    positive(first, result_newday);
    else
    negative(first, result_newday);
}

int main()
{
    setlocale(0, "rus");
    time first;
    calculator(first);
    system("pause");
    return 0;
}