日期类

        功能实现：在一个日期上+N天、-N天，重载前置++/--和后置++/--以及两个日期之间的差距，还有就是比较两个日期之间的大小。

#include<iostream>
using namespace std;
class Date
{
           friend ostream & operator<<(ostream& os, Date& d)//输出运算符重载
          {
                   os << d._year << "-" << d._month << "-" << d._day;
                    return os;
          }
public:
          Date( int year = 1900, int month = 1, int day = 1)//构造函数
                   :_year( year)
                   ,_month( month)
                   ,_day( day)
          {
                    if (Invalid())
                   {
                             _year = 1900;
                             _month = 1;
                             _day = 1;
                   }
          }
           //检查日期是否不合法
           bool Invalid()
          {
                    if (_year < 1900 || _month<1 || _month>12 || _day<0 || _day>GetMonthDay(_month))
                   {
                              return true ;
                   }
                    return false ;
          }
           //获取每月的天数
           int GetMonthDay(int month)
          {
                    int date[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
                    if (IsLeap())
                   {
                             date[2]+= 1;
                   }
                    return date[month ];
          }
           //判断是否是闰年
           bool IsLeap()
          {
                    if ((_year % 400 == 0) || ((_year % 4 == 0) && (_year % 100 != 0)))
                   {
                              return true ;
                   }
                    else
                              return false ;
          }
          Date( Date & d )//拷贝构造
          {
                   _year = d._year;
                   _month = d._month;
                   _day = d._day;
          }
           //修正日期
           void ToCorrect(Date & temp)
          {
                    while (temp ._day <= 0)
                   {
                              if (temp ._month == 1)
                             {
                                       temp._month = 12;
                                       temp._year--;
                             }
                              else
                             {
                                       temp._month -= 1;
                             }
                              temp._day += GetMonthDay(temp ._month);
                   }
                    while (temp ._day > GetMonthDay(temp._month))
                   {
                              temp._day -= GetMonthDay(temp ._month);
                              if (temp ._month == 12)
                             {
                                       temp._month = 1;
                                       temp._year++;
                             }
                              else
                             {
                                       temp._month++;
                             }
                   }
          }
           //日期加天数
           Date operator+(int day)
          {
                    Date temp(*this );
                   temp._day += day;
                   ToCorrect(temp);
                    return temp;

          }
           //日期减天数
           Date operator-(int day)
          {
                    Date temp(*this );
                   temp._day -= day;
                   ToCorrect(temp);
                    return temp;

          }
           //日期减日期
           int  operator-(Date & d)
          {
                    Date min(*this );
                    Date max(d );
                    if (min>max)
                   {
                             max = * this;
                             min = d;
                   }
                    int count=0;
                    while (min != max)
                   {
                             min++;
                             count++;
                   }
                    return count;
          }

           bool operator>(Date &d)
          {
                    if (_year > d ._year)
                   {
                              return true ;
                   }
                    else if ((_year = d._year) && (_month > d._month))
              {
                              return true ;
                   }
                    else if ((_year =d. _year) && (_month = d._month) && (_day > d._day))
                   {
                              return true ;
                   }
                    return false ;
          }
           bool operator==(Date & d)
          {
                    return _year == d ._year&&_month == d._month&&_day == d._day;
          }
           bool operator<(Date &d)
          {
                    return !(*this >d && * this == d );
          }
           bool operator!=(Date & d)
          {
                    return !(*this == d);
          }
           Date& operator=(Date & d)//赋值
          {
                   _year = d._year;
                   _month = d._month;
                   _day = d._day;
                    return *this ;
          }
           Date& operator+(Date & d)//加法
          {
                   _year += d._day;
                   _month += d._month;
                   _day += d._day;
                    return *this ;
          }
           Date& operator++()//前置++
          {
                   * this=*this +1;
                    return *this ;
          }
           Date operator++(int )//后置++
          {
                    Date temp(*this );
                   * this = *this + 1;
                    return temp;
          }
private:
           int _year;
           int _month;
           int _day;
};
int main()
{
           Date d1(2016, 4, 6);
          cout << d1 - 100 << endl;
           Date d2(1994, 3, 24);
          cout << d1 - d2 << endl;
          getchar();
           return 0;
}