How Can I overload operator >> and << correctly with cout and cin fucntions

[Unrepeatable]

How Can I overload operator >> and << correctly with cout and cin fucntions

#include <iostream>
#include <fstream>
using namespace std;

class Date {
private:
	unsigned int year;
	unsigned int month;
	unsigned int day;
public:
	Date() {
		year = 0;
		month = 12;
		day = 31;
	}
	Date(int y, int m, int d): year(y), month(m), day(d){		
	}
	Date& operator()(int hour, int min, int sec);
	int getDay()const  {
		return day;
	}
	int getMonth()const  {
		return month;
	}
	int getYear()const  {
		return year;
	}
	void increaseDay() {
		if (day == 31) {
			day = 1;
			month++;
		}
		else if (month == 12 && day ==31) {
			year++;
			day = 1;
			month = 1;
		}
		else {
			day++;
		}
	}
	Date& operator>>() {

	}
	Date& operator<<() {
		
	}
	Date& operator--() {
		if (day == 1) {
			day = 31;
			month--;
		}
		else if (month == 1 && day == 1) {
			year--;
			day = 31;
			month = 12;
		}
		else {
			day--;
		}
		return *this;
	}
	Date& operator++() {
		if (day == 31) {
			day = 1;
			month++;
		}
		else if (month == 12 && day == 31) {
			year++;
			day = 1;
			month = 1;
		}
		else {
			day++;
		}
		return *this;
	}

	Date& operator=(Date&obj){
		year = obj.year;
		month = obj.month;
		day = obj.day;
	}
	Date& operator +=(const Date&obj) {
		this->year += obj.year;
		this->month += obj.month;
		this->day += obj.day;
		return *this;
	 }
	Date& operator -=(const Date&obj) {
		this->year -= obj.year;
		this->month -= obj.month;
		this->day -= obj.day;
		return *this;
	}
	
};

Date& Date::operator()(int y, int m, int d) {
	this->year = y;
	this->month = m;
	this->day = d;
	return *this;
}

inline bool operator >(const Date&a, const Date&b) {
	if (a.getYear() > b.getYear() && a.getMonth() > b.getMonth() && a.getDay() > b.getDay()) {
		return true;
	}
	return false;
}
inline bool operator <(const Date&a, const Date&b) {
	if (a.getYear() < b.getYear() && a.getMonth() < b.getMonth() && a.getDay() < b.getDay()) {
		return true;
	}
	return false;
}

inline bool operator ==(const Date&a, const Date&b) {
	if (a.getYear() == b.getYear() && a.getMonth() == b.getMonth() && a.getDay() == b.getDay()) {
		return true;
	}
	return false;
}
inline bool operator!=(const Date&a, const Date&b) {
	return !(a == b);
}

int main() {
	Date k;
	cout << k.getDay()<<endl;
	k.increaseDay();
	cout << k.getDay();

	cin.get();
}

[keskiverto]

Look at how those operators are used:

std::cin >> foo;
std::cout << foo;

These are binary operators; two operands -- left and right.

If you write a member operator, it takes the right operand as argument and the class object is the left operand. Left operand of << and >> is iostream and you cannot add members to iostream.

You have to write the overloads as standalone functions.
See http://en.cppreference.com/w/cpp/language/operators
it shows:

std::ostream& operator<<(std::ostream& os, const T& obj)
{
    // write obj to stream
    return os;
}

std::istream& operator>>(std::istream& is, T& obj)
{
    // read obj from stream
    if( /* T could not be constructed */ )
        is.setstate(std::ios::failbit);
    return is;
}

Since these operators are not members' they have to either use public interface of the class, or be friends of the class.