// File: ex7-2.cpp – Adding functionality to a class using inheritance

#include <iostream>
using namespace std;

class Number
{
protected:
    int x;
public:
    Number() {}
    Number(int n) : x(n) { }
    Number(const Number& n) : x(n.x) { }
    int get_x() const
    {
        return x;
    }
    Number& operator=(const Number& z)
    {
        x = z.x;
        return *this;
    }
    Number  operator+(const Number& y) const
    {
        return x + y.x;
    }
};

ostream& operator<<(ostream& out, const Number& obj)
{
    out << obj.get_x();
    return out;
}

class MyNumber : public Number
{
public:
    MyNumber() {}
    MyNumber(int n) : Number(n) { }
    MyNumber(const Number& n) : Number(n) {}
    MyNumber(const MyNumber& m) : Number(m) {}
    MyNumber  operator-(const MyNumber& y) const
    {
        return x - y.x;
    }
};

int main(void)
{
    Number n1(4), n2(5);
    Number n3;
    cout << "n1=" << n1 << endl;
    cout << "n2=" << n2 << endl;
    n3 = n1 + n2;
    cout << "n3=" << n3 << endl;
    cout << endl;

    MyNumber mn1(7), mn2(4);
    MyNumber mn3;
    cout << "mn1=" << mn1 << endl;
    cout << "mn2=" << mn2 << endl;

    mn3 = mn1 + mn2;
    cout << "mn3=" << mn3 << endl;

    mn3 = mn1 - mn2;
    cout << "mn3=" << mn3 << endl;

    MyNumber mn4(n1);
    cout << "mn4=" << mn4 << endl;

    MyNumber mn5(mn1);
    cout << "mn5=" << mn5 << endl;
}