C++ Implementation date class (Date)

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#include<iostream>
#include<stdlib.h>
using namespace std;
class Date
{
public:
 // The constructor 
 Date(int year = 1900, int month = 1, int day = 1)
 :_year(year)
 , _month(month)
 , _day(day)
 {
 if (!IsInvalidDate(_year, _month, _day))
 {
  _year = 1900;
  _month = 1;
  _day = 1;
 }
 }
 // Copy function 
 Date(const Date& d)
 : _year(d._year)
 , _month(d._month)
 , _day(d._day)
 {}
 
 // The destructor 
 ~Date()
 {}
 
 // Decide if it's a leap year 
 bool IsLeapYear(int year)
 {
  if ((year % 400 == 0) ||
  ((year % 4 == 0) && (year % 100 != 0)) )
  {
  return true;
  }
  return false;
 }
 // Determine if the date is valid 
 bool IsInvalidDate(int year, int month, int day)
 {
  if ((year < 1) ||
  (month < 0 || month >12) ||
  (day < 0 || day > YearsOfMonth(year, month)))
  {
  return false;
  }
  return true;
 }
 // Determine the number of days in the current month 
 int YearsOfMonth(int year, int month)
 {
  int day;
  int days[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
  day = days[month];
  if (month == 2 && IsLeapYear(year))
  {
  day += 1;
  }
  return day;
 }
 // Revision date 
 Date ToCorrect(Date &d)
 {
  while (d._day > YearsOfMonth(d._year, d._month) || d._day <= 0)
  {
  if(d._day <= 0)
  {
   d._day += YearsOfMonth(d._year,( d._month - 1));
   if (d._month == 1)
   {
   d._month = 12;
   d._year--;
   }
   else
   {
   d._month--;
   }
  }
  else
  {
   d._day -= YearsOfMonth(d._year, d._month);
   if (d._month == 12)
   {
   d._year++;
   d._month = 1;
   }
   else
   {
   d._month++;
   }
  }
  }
  return d;
 }
 //  The current date days What's the date?  
 Date operator+(int days)
 {
  Date tmp(*this);
  tmp._day += days;
  ToCorrect(tmp);
  return tmp;
 }
 
 //  The current date days What date was it ten days ago?  
 Date operator-(int days)
 {
  Date tmp(*this);
  tmp._day -= days;
  ToCorrect(tmp);
  return tmp;
 }
 
 //  Date ratio size  
 bool operator>(const Date& d)
 {
 return ( _year > d._year || 
  (_year == d._year && _month > d._month) ||
  (_year == d._year && _month == d._month && _day > d._day));
 }
 bool operator<(const Date& d)
 {
 return (_year < d._year ||
  (_year == d._year && _month < d._month) ||
  (_year == d._year && _month == d._month && _day < d._day));
 }
 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)
 {
 return !(*this<d);
 }
 bool operator<=(const Date &d)
 {
 return !(*this>d);
 }
 
 //  Overload take address symbol  
 Date* operator&()
 {
 
 }
 
 //  Pre - ++ 
 Date& operator++()
 {
 (*this)++;
 return *this;
 }
 
 //  The rear ++ 
 Date operator++(int)// Distinguish between prepositions and postpositions by return values and pass arguments ++
 {
 Date tmp(*this);
 (*this) = (*this) + 1;
 return tmp;
 }
 
 //  Pre - -- 
 Date& operator--()
 {
 (*this)--;
 return *this;
 }
 
 //  The rear -- 
 Date operator--(int)
 {
 Date tmp(*this);
 (*this)--;
 return tmp;
 }
 void Display()
 {
 cout << _year << "-" << _month << "-" << _day << endl;
 }
private:
 int _year;
 int _month;
 int _day;
};
 
int main()
{
 Date d(2018, 9, 9);
 d.Display();
 Date d1 = d + 50;
 d1.Display();
 d1 =d1 - 50;
 d1.Display();
 
 cout << "------"<<endl;
 cout << " Pre - ++" << endl;
 d1.Display();
 (++d1).Display();
 d1.Display();
 cout << " The rear ++" << endl;
 d1.Display();
 (d1++).Display();
 d1.Display();
 cout << "------" << endl;
 
 
 system("pause");
 return 0;
}