Дата

// https://otvet.mail.ru/question/217374813
#include <iostream>
using namespace std;
struct Date {
    int year;
    int month;
    int day;
    Date() : year(1900), month(1), day(1) {}
    Date(int y, int m, int d) : year(y), month(m), day(d) {
        if ((month > 12 || month <= 0 || day <= 0 || year <= 0)
            || (isLeapYear() && day > leap[month])
            || (!isLeapYear() && day > months[month])) {
            year = 1900;
            month = day = 1;
        }
    }
    static const int months[13];
    static const int leap[13];
    bool isLeapYear() {
        bool result;
        if (year % 4 != 0) result = false;
        else if (0 == year % 400) result = true;
        else if (0 == year % 100) result = false;
        else result = true;
        return result;
    }
    int monthDays() {
        if (isLeapYear()) return leap[month];
        return months[month];
    }
    void tonextDate() {
        if (!isLeapYear() && day != months[month]) ++day;
        else if (isLeapYear() && day != leap[month]) ++day;
        else if (month < 12) {
            ++month;
            day = 1;
        } else {
            ++year;
            month = day = 1;
        }
    }
    void toprevDate() {
        if (day != 1) --day;
        else {
            if (month != 1) --month;
            else {
                --year;
                month = 12;
                day = 31;
            }
            if (isLeapYear()) day = leap[month];
            else day = months[month];
        }
    }
    void addDays(int d) {
        if (d <= 0) return;
        for (int i = 0; i < d; ++i) tonextDate();
    }
    void delDays(int d) {
        if (d <= 0) return;
        for (int i = 0; i < d; ++i) toprevDate();
    }
    int cmpDate(Date date) {
        auto is_equal = [this, &date]() {
            return year == date.year && month == date.month && day == date.day;
        };
        auto is_less = [this, &date]() {
            if (year < date.year) return true;
            else if (year == date.year && month < date.month) return true;
            else if (year == date.year && month == date.month && day < date.day) return true;
            return false;
        };
        if (is_equal()) return 0;
        int diff = 0;
        if (is_less()) {
            while (!is_equal()) {
                date.toprevDate();
                ++diff; // если дата, переданная в качестве параметра больше
            }
        } else {
            while (!is_equal()) {
                date.tonextDate();
                --diff; // если дата, переданная в качестве параметра меньше
            }
        }
        return diff;
    }
    friend ostream& operator<<(ostream& out, const Date& date) {
        out << date.year << '-';
        if (date.month < 10) out << '0';
        out << date.month << '-';
        if (date.day < 10) out << '0';
        out << date.day;
        return out;
    }
};
const int Date::months[13] = { 365, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
const int Date::leap[13] = { 366, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
int main() {
    Date a(2019, 11, 24);
    cout << a << '\n';
    cin.get();
}