C++实现Date

#include<iostream>
using namespace std;
class Date
{
public:
    Date(int year = 1900,int month = 1,int day = 1)
        :_year(year)
        ,_month(month)
        ,_day(day)
    {
    }
    Date(Date &day)
    {
        _year = day._year;
        _month = day._month;
        _day = day._day;
    }
    ~Date()
    {

    }
    void Display(Date &day)
    {
        cout<<day._year<<" "<<day._month<<" "<<day._day<<endl;
    }
    int GetMonDay(int year,int month)
    {
        static int monthArr[12] = {31,28,31,30,31,30,31,31,30,31,30,31};

        int day = monthArr[month - 1];
        if((month == 2) && (year%400 == 1 || (year%4 == 1 && year%100 != 1)))
        {
            day++;
        }

        return day;
    }
    bool operator==(Date day2)
    {
        return     (this->_year == day2._year)&&
         (this->_month = day2._month)&&
         (this->_day = day2._day);
    }
    int operator-(Date d)//?????????à?????ì??
    {
        Date tmp;
        //±??¤this???ò???ó????
        if ((this->_year > d._year) || (this->_year == d._year && this->_month > d._month)||
            (this->_year == d._year && this->_month == d._month && this->_day > d._day))
        {
            tmp = d;
            d = *this;
            *this = tmp;
        }
        int MonDay[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
        //???????ó?????ù??????×?
        int Diff1 = _day - 1;
        for(int i =_month; i > 1; i--)
        {
            Diff1 += MonDay[i - 1];
            if((i == 2) && (_year%400 == 0 || (_year%4 == 0 && _year%100 != 0)))
            {
                Diff1++;
            }
        }
     //???????°??×??ù??????×?
        int Diff2 = d._day - 1;
        for(int j = d._month; j > 1; j--)
        {
            Diff2 += MonDay[j - 1];
            if((j == 2) && (d._year%400 == 0 || (d._year%4 == 0 && d._year%100 != 0)))
            {
                Diff2++;
            }
        }
        if(d._year > _year)
        {
            for(int i = d._year; i > _year; i--)
            {
                Diff2 += 365;
                if(i%400 == 0 || (i%4 == 0 && i%100 != 0))
                {
                    Diff2++;
                }
            }
        }
        int Diff = Diff2 - Diff1;
        return Diff;
    }
//??????·?·¨??°???????×??????????????í??????×??????????????ù???ì??
//    int operator-(const Date& d)
//    {
//        int flag = 1;
//        Date max = *this;
//        Date min = d;
//
//        if (*this < d)
//        {
//            min = *this;
//            max = d;
//            flag = -1;
//        }
//
//        int days = 0;
//        //while (min._year < max._year)
//        //{
//            //days += 365;
//            //if () // ?ó?ê
//            //{
//            //}
//        //}
//
//        while (min != max)
//        {
//            ++min;
//            days++;
//        }
//
//        return flag*days;
//    }
    Date& operator+(int day)
    {
        if(day < 0)
        {
            return *this - (-day);
        }
        _day += day;
        while(_day > GetMonDay(_year,_month))
        {
            if(_month < 12)
            {
                _month++;
                _day -= GetMonDay(_year,_month);
            }
            else
            {
                _year++;
                _month = 1;
                _day -= GetMonDay(_year,_month);
            }
        }
        return *this;
    }
    Date& operator-(int day)
    {
        if(day < 0)
        {
            return *this + (-day);
        }
        _day -= day;
        while(_day < 1)
        {
            if(_month == 1)
            {
                _year--;
                _month += 12;
                _day += GetMonDay(_year,_month);
            }
            else
            {
                _month--;
                _day += GetMonDay(_year,_month);
            }
        }
        return *this;
    }
    Date& operator+=(int days)
     {
         *this = *this + days;
         return *this;
     }

     Date& operator-=(int days)
     {
         *this = *this - days;
         return *this;
     }

    Date& operator++()
    {
        if(_day == GetMonDay(_year,_month))
        {
            if(_month == 12)
            {
                _year++;
                _month = 1;
                _day = 1;
            }
            _month++;
            _day = GetMonDay(_year,_month);
        }
        _day++;
        return *this;
    }
    Date operator++(int)
    {
        Date *tmp = this;
        if(_day == GetMonDay(_year,_month))
        {
            if(_month == 12)
            {
                _year++;
                _month = 1;
                _day = 1;
            }
            _month++;
            _day = GetMonDay(_year,_month);
        }
        _day++;
        return *tmp;
    }

    Date& operator--()
    {
        if(_day = 1)
        {
            if(_month = 1 )
            {
                _year--;
                _month = 12;
                _day = GetMonDay(_year,_month);
                return *this;
            }
            _month--;
            _day = GetMonDay(_year,_month);
            return *this;
        }
        _day--;
        return *this;
    }
    Date operator--(int)
    {
        Date *tmp = this;
        if(_day = 1)
        {
            if(_month = 1 )
            {
                _year--;
                _month = 12;
                _day = GetMonDay(_year,_month);
                return *this;
            }
            _month--;
            _day = GetMonDay(_year,_month);
            return *this;
        }
        _day--;
        return *tmp;
    }
    istream& operator>>(istream& is, Date& d)
    {
        cout<<"?????????????????ê????:";
        is>>d._year>>d._month>>d._day;

        return is;
    }

    ostream& operator<<(ostream& os, const Date& d)
    {
        cout<<d._year<<"-"<<d._month<<"-"<<d._day<<endl;
        return os;
    }
private:
    int _year;
    int _month;
    int _day;
};