【c++】用c++實現Date類

#include<iostream>
#include<assert.h>
using namespace std;

class Date
{
public:
	Date(int year = 1900, int month = 1, int day = 1)
		:_year(year),_month(month),_day(day)
	{
	    assert(year >= 1900);
		assert(month > 0 && month < 13);
		assert(day > 0 && day <= GetMonDay(year, month));
	}
	//賦值運算符重載
	Date& operator=(const Date& d)
	{
	 if(*this != d)
	 {
	  _year = d._year;
	  _month = d._month;
	  _day = d._day;
	 }
	 return *this;
	}
	//計算一個日期加減一個天數的運算符重載
	Date operator+(int day)
	{ 
	  Date tmp(*this); 
	  if(day<0)
	  {
	   day = -day;
	   return (tmp - day);
	  }
	  if(day == 0)
	  {
	   return tmp;
	  }
	  else
	    tmp._day += day;
	    if(tmp._day > GetMonDay(tmp._year,tmp._month))
		{
	       tmp._day -= GetMonDay(tmp._year,tmp._month);
           if(tmp._month == 12)
		   {
		      tmp._year++;
		      tmp._month = 1;
		   }
		   else
		   {
		     tmp._month++;
		   }
		}
	 return tmp;
	}
	Date operator+=(int day)
	{
	  Date tmp(*this);
	  tmp = *this + day;
	  *this = tmp;
	  return *this;
	}
	Date operator-(int day)
	{ 
	  Date tmp(*this);
	  if(day<0)
	  {
	     day = -day;
		 return(tmp + day);
	  }
	  if(day == 0)
	  {
	     return tmp;
	  }
	  else
		  tmp._day -= day;
	      while(tmp._day<=0)
		  {
		   if(tmp._month == 1)
		   {
		    tmp._year--;
            tmp._month = 12;
		   }
		   else
		   {
		    tmp._month--;
		   }
		   tmp._day = GetMonDay(tmp._year,tmp._month)+tmp._day;
		  }
	  return tmp;
	}
	Date operator-=(int day)
	{
	 Date tmp(*this);
	 tmp = *this - day;
	 *this = tmp;
	 return *this;
	}
    Date operator++()
	{
	 *this += 1;
	 return *this;
	}
	Date operator++(int)//後置++
	{
	 Date tmp(*this);
	 *this += 1;
	 return tmp;
	}
	Date operator--()
	{
	 *this -= 1;
	 return *this;
	}
	Date operator--(int)//後置--
	{
	 Date tmp(*this);
	 *this -= 1;
	 return tmp;
	}
	//比較運算符的重載
	bool operator==(const Date& d)
	{
	 return (_year == d._year && _month == d._month && _day == d._day);
	}
	bool operator!=(const Date &d)
	{
	 return !(*this == d);
	}
	bool operator >(const Date& d)
	{
	 if(_year > d._year)
	 {
	    return true;
	 }
	 if(_year == d._year)
	 {
	    if(_month > d._month)
		{
			 return true;
		}
		if(_month == d._month)
		{
			if(_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);
	}
	int GetMonDay(int year, int month)
	{
	    assert(year >= 1900);
		assert(month > 0 && month < 13);
		static int monthArray[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
		int day = monthArray[month];
        if((month == 2) && (year%400 || (year%4 && year%100)))
		{
		    day+=1;
		}
		return day;
	}
	//計算兩個日期相減
	int operator-(const Date& d)
	{
	 int count = 0;
	 Date d1 = *this;
	 Date d2 = d;
	 if(*this > d)
	 {
	  d1 = d;
	  d2 = *this;
	 }
	 while(d1!=d2)
	 {
	  d1+=1;
	  count++;
	 }
	 return count;
	}

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

private:
	int _year;
	int _month;
	int _day;
};

void Test()
{
 Date d1(2015,12,1);
 Date d2(2015,12,23);
 int count;
 count = d2-d1;
 cout<<count<<endl;
 d2 = d1;
 d2.Display();
 //cout<<(d1==d2)<<endl;
 //cout<<(d1!=d2)<<endl;
 //cout<<(d1>d2)<<endl;
 //cout<<(d1>=d2)<<endl;
 //cout<<(d1<d2)<<endl;
 //cout<<(d1<=d2)<<endl;

// d.Display();
}
int main()
{

Test();
return 0;
}