#pragma once
#include <iostream>

using namespace std;
#ifndef _DATE_HPP_
#define _DATE_HPP_

class Date
{
private:
    size_t day;
    size_t month;
    size_t year;

public:
    Date() : day(1), month(1), year(1970) {};
    Date(size_t day, size_t month, size_t year) :
        day(day),
        month(month),
        year(year)
    {};

    Date(const Date &obj) :
        day(obj.day),
        month(obj.month),
        year(obj.year)
        {};

    // Destructor
    virtual ~Date();

    // Get Methods
    inline auto getDay() -> size_t {
        return this->day;
    };

    inline auto getMonth() -> size_t {
        return this->month;
    };

    inline auto getYear() -> size_t {
        return this->year;
    };

    // Set Methods

    inline auto setDay(size_t value) -> void {
        this->day = value;
    }

    inline auto setMonth(size_t value) -> void {
        this->month = value;
    }

    inline auto setYear(size_t value) -> void {
        this->year = value;
    }

    inline auto operator < (Date &obj) -> bool {
        //return ((this->year < obj.year) ? true : this->month < obj.month ? true : this->day < obj.day ? true : false );
        return (this->year < obj.year || this->month < obj.month || this->day < this->day);
    }

    inline auto operator== (const Date &obj) -> bool {
        return (this->year == obj.year && this->month == obj.month && this->day == obj.day);
    }

    auto operator+(size_t count) -> Date {
        do {
            if(this->day + count > 31) {

                if(this->month % 2 == 0 && this->month != 12)
                    this->day = ((this->day + count) - 30);
                else
                    this->day = ((this->day + count) - 31);


                if(this->month > 11) {

                    this->month = 1;
                    this->year++;
                }
            }
        } while(this->day > 31);

        return *this;
    }

    auto operator-(size_t count) -> Date {
        this->day -= 20;
        return *this;
    }

    auto operator+=(size_t count) -> Date {
        if(this->day + count > 31) {

            if(this->month % 2 == 0 && this->month != 12)
                this->day = ((this->day + count) - 30);
            else
                this->day = ((this->day + count) - 31);


            if(this->month > 11) {

                this->month = 1;
                this->year++;
            }
        }

        return *this;
    }

    friend auto operator <<(ostream &output, const Date &obj) -> ostream& {
        output << obj.day << "/" << obj.month << "/" << obj.year;

        return output;
    }
};


#endif

--------------

#pragma once

#include "Date.hpp"

#include <string>

#ifndef _LIBRARY_HPP_
#define _LIBRARY_HPP_

class Library
{
private:
    string id;
    string reader;
    Date date;

public:
    Library() : id(""), reader(""), date(Date()) {};
    Library(string id, string reader, Date &date) :
        id(id),
        reader(reader),
        date(date) {};

    Library(const Library &obj) :
        id(obj.id),
        reader(obj.reader),
        date(obj.date) {};

    // Destructor
    virtual ~Library(void);

    // Get Methods
    inline auto getId() -> string {
        return this->id;
    }

    inline auto getReader() -> string {
        return this->reader;
    }

    inline auto getDate() -> Date& {
        return this->date;
    }

    // Operators
    auto operator<(Library &obj) -> bool {
        return (this->date < obj.date);
    }

    auto operator==(const Library &obj) -> bool {
        return (this->id == obj.id && this->reader == obj.reader && this->date == obj.date);
    }

    friend auto operator<<(ostream &output, const Library &obj) -> ostream& {

        output << "Book ID: " << obj.id << endl;
        output << "Reader Name: " << obj.reader << endl;
        output << "Date: " << obj.date << endl;

        return output;
    }

};

#endif

----------------

#include "Library.hpp"

#include <vector>
#include <algorithm>

int main() {

    vector<Library> array_libraries;
    vector<Date> array_date;
    Date now(11, 12, 2018);

    array_date.push_back(Date(25, 10, 2018));
    array_date.push_back(Date(5, 12, 2019));

    array_libraries.push_back(Library("1", "Georgi", array_date[1]));
    array_libraries.push_back(Library("2", "Petur", array_date[0]));

    for(auto &element : array_libraries) {
        cout << element;
    }

    sort(array_libraries.begin(), array_libraries.end(), [](Library &left, Library &right) {
        return left.getDate() < right.getDate();
    });

    cout << "\n\nSorted: \n\n";

    for(auto &element : array_libraries) {
        cout << element;
    }

    cout << "\n\nLate: \n\n";

    for(auto &element :array_libraries) {

        if(element.getDate() < (now -20)) {
            cout << element;
        }
    }

    return 0;
}