C++实现一个日期类

#include "Date.h"
void Date::display()
{
cout << _year << "-" << _month << "-" << _day << endl;
}

int GetMonthDay(int year, int month)
{
static int MonthDay[13] = { 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
if (month == 2)
{
if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
{
return MonthDay[month] - 1;
}
}
return MonthDay[month];
}

bool Date::IsLegal()
{
if ((_year >= 0) && (_month > 0) && (_month
< 13) && (_day>0) && (_day <= GetMonthDay(_year, _month)))
{
return true;
}
else
{
return false;
}
}

Date Date:: operator+(int day)   //不改变初始日期的值
{
if (day < 0)
{
return *this - (-day);
}
Date tmp = *this;
tmp._day += day;
while (tmp._day > GetMonthDay(tmp._year, tmp._month))
{
tmp._day = tmp._day - GetMonthDay(tmp._year, tmp._month);
if (tmp._month == 12)
{
tmp._month = 1;
tmp._year += 1;
}
else
{
tmp._month += 1;
}
}
return  tmp;
}

Date & Date::operator+=(int day)
{
*this = *this + day;    //代码的复用
return *this;
}

Date Date::operator-(int day)  //减去多少天，不改变初始日期的值
{
if (day < 0)  //d1-(-100)
{
return *this + (-day);
}
Date tmp = *this;
tmp._day = tmp._day - day;
while (tmp._day <= 0)
{
if (tmp._month == 1)
{
tmp._month = 12;
tmp._year -= 1;
}
else
{
tmp._month -= 1;
}
tmp._day = tmp._day + GetMonthDay(tmp._year, tmp._month);
}
return tmp;
}

bool Date:: operator==(const Date&d) //比较日期大小
{
if ((_year != d._year) || (_month != d._month) || (_day != d._day))
{
return  false;
}
return  true;
}

bool Date:: operator!=(const Date&d) //比较日期大小
{
return !((*this).operator==(d));
}

Date & Date :: operator-=(int day)  //减去多少天，改变初始日期的值
{
*this = *this - day;
return *this;
}

bool Date::operator> (const Date&d)  //比较日期大小
{
if ((this->_year>d._year)
|| ((this->_month>d._month)&&(this->_year==d._year))
||((this->_day>d._day)&&(this->_month==d._month)&&(this->_year==d._year)))
{
return true;
}
return false;
}

Date Date:: operator++(int)     //date++；
{
Date tmp = *this;
*this += 1;
return  tmp;
}

Date & Date:: operator++()     //date++；
{
*this += 1;
return  *this;
}

int  Date::operator-(const Date&d)   //两个日期相减相差多少天
{
Date FutureDay;
Date PastDay;
int i = 0;
if (*this > d)
{
FutureDay = *this;
PastDay = d;
}
else
{
FutureDay = d;
PastDay = *this;
}
while (FutureDay != PastDay)
{
PastDay += 1;
i++;
}
return i;
}

#define _CRT_SECURE_NO_WARNINGS
#ifndef  __DATE_CLASS__
#define __DATE_CLASS__

#include <iostream>
#include <windows.h>
#include <assert.h>
using namespace std;
class Date
{
public:
Date(int year=1995,int month=5 ,int day=6)
:_year(year)
, _month(month)
, _day(day)
{
assert(IsLegal());
}

void display();  //打印日期

Date operator+(int day);  //加上多少天，不改变初始日期的值

Date & operator+=(int day);  //加上多少天，改变初始日期的值

Date operator-(int day);  //减去多少天，不改变初始日期的值

Date & operator-=(int day);  //减去多少天，改变初始日期的值

bool operator>(const Date&d);  //比较日期大小

bool operator==(const Date&d);  //比较日期大小

bool operator!=(const Date&d);  //比较日期大小

Date operator++(int);     //date++；

Date & operator++();       //++date;

int operator-(const Date&d);   //两个日期相减相差多少天

bool IsLegal();    //判断日期是否合法
private:
int _year;
int _month;
int _day;
};

#include "Date.h"
int main()
{
Date d(2017,3,8);
Date d1 = d + 100;
d.display();
d1.display();
Date d2(2017, 3, 8);
d2 += 100;
d2.display();
Date d3 = d2 - (-100);
d3.display();
Date d4 = d3 + (-100);
d4.display();
int k=d3 > d4;
cout << k << endl;
Date d5 = d4;
(d5++).display();
(++d5).display();
int a = d3 - d4;
cout << a << endl;
system("pause");
return 0;
}