C++ class task

cpp-03-13-2021.cpp

#include <iostream>

class Number {
public:
    virtual void print(std::ostream& os) const = 0;
    virtual Number* sum(const Number& other) const = 0;
};
std::ostream& operator <<(std::ostream& os, const Number& n) { n.print(os); return os; }

class NaturalNumber : public Number
{
    int n;
public:
    NaturalNumber (int n_) : n(n_) {}
    int getValue() const { return n; }
    virtual void print(std::ostream& os) const { std::cerr << "NaturalNumber::print()"; os << n; }
    virtual Number* sum(const Number& other) const;
};

class Signed {
public:
    virtual void switchSign() = 0;
};

class IntegerNumber : public Number, public Signed
{
    int n;
public:
    IntegerNumber(int n_) : n(n_) {}
    int getValue() const { return n; }
    virtual void print(std::ostream& os) const { std::cerr << "IntegerNumber::print()"; os << n; }
    virtual void switchSign() { n = -n; }
    virtual Number* sum(const Number& other) const;
};

class RealNumber : public Number, public Signed
{
    double n;
public:
    RealNumber (double n_) : n(n_) {}
    double getValue() const { return n; }
    virtual void print(std::ostream& os) const { std::cerr << "RealNumber::print()"; os << n; }
    virtual void switchSign() { n = -n; }
    virtual Number* sum(const Number& other) const;
};

Number* IntegerNumber::sum(const Number& other) const {
    const NaturalNumber* nn = dynamic_cast<const NaturalNumber*>(&other);
    if (nn != NULL)
        return new IntegerNumber(n + nn->getValue());
    const IntegerNumber* in = dynamic_cast<const IntegerNumber*>(&other);
    if (in != NULL)
        return new IntegerNumber(n + in->getValue());
    const RealNumber* rn = dynamic_cast<const RealNumber*>(&other);
    if (in != NULL)
        return new RealNumber(n + in->getValue());
}

Number* RealNumber::sum(const Number& other) const {
    const NaturalNumber* nn = dynamic_cast<const NaturalNumber*>(&other);
    if (nn != NULL)
        return new RealNumber(n + nn->getValue());
    const IntegerNumber* in = dynamic_cast<const IntegerNumber*>(&other);
    if (in != NULL)
        return new RealNumber(n + in->getValue());
    const RealNumber* rn = dynamic_cast<const RealNumber*>(&other);
    if (in != NULL)
        return new RealNumber(n + in->getValue());
}

IntegerNumber operator +(const IntegerNumber &n1, const NaturalNumber &n2)
{
    return IntegerNumber(n1.getValue() + n2.getValue());
}
IntegerNumber operator +(const NaturalNumber&n1, const IntegerNumber&n2)
{
    return IntegerNumber(n1.getValue() + n2.getValue());
}
// ...

int main()
{
    NaturalNumber nn(12); RealNumber rn(4.2); Signed* s = &rn; s->switchSign();
    std::cout << "Natural: " << nn << std::endl;
    std::cout << "Real: " << rn << std::endl;
}