用C++实现日期类

用C++实现日期类，其中包含 日期加上天数结果为一个新日期，日期减去一个天数结果为新日期，两个日期相减结果为相差的天数等等函数的实现。

#pragma once
#include 
   
    
#include 
    
     
using namespace std;

class Date
{
private:
	int _year;
	int _month;
	int _day;
public:
	Date(int year=1900, int month=1, int day=1)
		:_year(year), _month(month), _day(day)
	{
		assert(IsInvalid());
	}

	void Display()
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}

	bool IsInvalid()
	{
		if (_year >= 1900 && _month > 0 && _month<13 && _day>0 && _day <= GetMonthDays(_year, _month))
		{
			return true;
		}
		return false;
	}

	int GetMonthDays(int year, int month)         //计算每个月的天数
	{
		int monthDays[13] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
		if (month != 2)
		{
			return monthDays[month];
		}
		else
		{
			if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))
			{
				return 29;
			}
			else
			{
				return 28;
			}
		}
	}

	Date operator+(int day)                 //计算一个日期加上天数结果为一个日期
	{
		if (day < 0)
		{
			return *this - (-day);
		}
		Date tmp(*this);
		tmp._day += day;
		while (tmp.IsInvalid() == false)
		{
			tmp._day -= GetMonthDays(tmp._year, tmp._month);
			if (tmp._month == 12)
			{
				tmp._year++;
				tmp._month = 1;
			}
			else
			{
				tmp._month++;
			}
		}
		return tmp;
	}
	Date operator-(int day)                  //计算日期减去一个天数结果为一个日期
	{
		if (day < 0)
		{
			return *this + (-day);
		}
		Date tmp(*this);
		tmp._day -= day;
		while (tmp.IsInvalid() == false)
		{
			if (tmp._month == 1)
			{
				tmp._year--;
				tmp._month = 12;
			}
			else
			{
				tmp._month--;
			}
			int day = GetMonthDays(tmp._year, tmp._month);
			tmp._day += day;
		}
		return tmp;
		}

	inline Date& operator+=(int day)
	{
		*this = *this + 100;
		return *this;
	}

	inline Date& operator-=(int day)
	{
		*this = *this - 100;
		return *this;
	}

	inline Date& operator++()          //前加加
	{
		*this += 1;
		return *this;
	}
	inline Date operator++(int)         //后加加
	{
		Date tmp(*this);
		*this += 1;
		return tmp;
	}

	inline Date& operator--()           //前减减
	{
		*this -= 1;
		return *this;
	}

	inline Date operator--(int)           //后减减
	{
		Date tmp(*this);
		*this -= 1;
		return tmp;
	}

	bool operator >(const Date& d)      //比较大小
	{
		if (_year > d._year || (_year == d._year && (_month > d._month || (_month == d._month&&_day > d._day))))
		{
			return true;
		}
		return false;
	}
	bool operator>=(const Date& d)
	{
		return *this > d || *this == d;
	}

	bool operator<(const Date& d)
	{
		return!(*this >= d);
	}

	bool operator<=(const Date& d)
	{
		return (*this > d);
	}

	bool operator==(const Date& d)
	{
		return _year == d._year
		&&_month == d._month
		&&_day == d._day;
	}

	bool operator!=(const Date& d)
	{
		return !(*this == d);
	}

	int operator-(const Date& d)          //计算两个日期之差为天数
	{
		int sum1 = 0;
		int sum2 = 0;
		int sum3 = 0;
		int sum = 0;
		int month = 0;
		int year = 0;
		for (month = 1; month < _month; month++)
		{
			sum1 += GetMonthDays(_year, month);
		}
		sum1 += _day;
		
		for (month = 1; month < d._month; month++)
		{
			sum2 += GetMonthDays(d._year, month);
		}
		sum2 += d._day;
	    sum3 = abs(sum1 - sum2);
		if (_year == d._year)
		{
			return sum3;
		}
		else if (_year > d._year)
		{
			for (year = d._year; year < _year; year++)
			{
				if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
				{
					sum += 366;
				}
				else
				{
					sum += 365;
				}
			}
				return abs(sum - sum3);
			
		}
		else if (_year < d._year)
		{
			for (year = _year; year < d._year; year++)
			{
				if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
				{
					sum3 += 366;
				}
				else
				{
					sum3 += 365;
				}
			}
				return abs(sum - sum3);
		}
	}
};

void TestDate()
{
	Date d1(2017,3,9);
	d1.Display();

	Date d2(2008,4,20);
	d2.Display();

	int d3 = d1 - d2;
	cout <<"两个日期相差的天数为：" <
     
      << endl;
    
	/*Date d2 = d1 +100;
	d2.Display();

	Date d3 = d2 - 100;
	d3.Display();*/
	
}

test.c
#include "Date.h"
int main()
{
	TestDate();
	return 0;
}