13.6 Overloading unary operators +, -, and !

Overloading uary operators

#include <iostream>

class Cents
{
private:
    int m_cents {};

public:
    Cents(int cents): m_cents(cents) {}

    // Overload -Cents as a member function
    Cents operator-() const;

    int getCents() const { return m_cents; }
};

// note: this function is a member function!
Cents Cents::operator-() const
{
    return -m_cents; // since return type is a Cents, this does an implicit conversion from int to Cents using the Cents(int) constructor
}

int main()
{
    const Cents nickle{ 5 };
    std::cout << "A nickle of debt is worth " << (-nickle).getCents() << " cents\n";

    return 0;
}

#include <iostream>

class Point
{
private:
    double m_x {};
    double m_y {};
    double m_z {};

public:
    Point(double x=0.0, double y=0.0, double z=0.0):
        m_x{x}, m_y{y}, m_z{z}
    {
    }

    // Convert a Point into its negative equivalent
    Point operator- () const;

    // Return true if the point is set at the origin
    bool operator! () const;

    double getX() const { return m_x; }
    double getY() const { return m_y; }
    double getZ() const { return m_z; }
};

// Convert a Point into its negative equivalent
Point Point::operator- () const
{
    return { -m_x, -m_y, -m_z };
}

// Return true if the point is set at the origin, false otherwise
bool Point::operator! () const
{
    return (m_x == 0.0 && m_y == 0.0 && m_z == 0.0);
}

int main()
{
    Point point{}; // use default constructor to set to (0.0, 0.0, 0.0)

    if (!point)
        std::cout << "point is set at the origin.\n";
    else
        std::cout << "point is not set at the origin.\n";

    return 0;
}