Rectangle

#include <cmath>
#include <cstdlib>
#include <string>
#include <iostream>
#include <cmath>


using namespace std;

/*
 *
 * — Существует ли объектно-ориентированный способ стать богатым?
 * — Да, наследование.
 *
 */

class NegativeException {
    string exc;

    friend ostream& operator<<(ostream& os, const NegativeException& vi) {
        os << "исключение " << vi.exc;
        return os;
    }
public:

    NegativeException() {
        this->exc = "NegativeException";
    }
};

class Rectangle {
    double a, b;
public:

    Rectangle(double a, double b) {
        if (a <= 0 || b <= 0) throw NegativeException();
        this->a = a;
        this->b = b;
    }

    Rectangle(double a) {
        if (a <= 0)throw NegativeException();
        this->a = a;
        this->b = a;
    }

    Rectangle() {
        this->a = 1;
        this->b = 1;
    }

    double s() {
        return a*b;
    }

    double p() {
        return 2 * a + 2 * b;
    }

    bool equals(Rectangle a) {
        if ((this->a == a.a && this->b == a.b) || (this->a == a.b && this->b == a.a))return true;
        return false;
    }

    bool operator==(Rectangle a) {
        return this->equals(a);
    };

    bool operator!=(Rectangle a) {
        return !(this->equals(a));
    };

    void operator=(Rectangle b) {
        this->a = b.a;
        this->b = b.b;
    };

    friend ostream& operator<<(ostream& os, const Rectangle& at) {
        os << "a=" << at.a << ", b=" << at.b;
        return os;
    };
};