C ++非成员函数，使用引用另一个类的类

Question

I have this HW question that I have been stuck for hours on that I can't seem to make sense of. It's kind of hard to put to words my actual question but I will try my best. How can I make my outside-member function find the distance between a circle using a class which references another class? In my code below:

//Header
class Point
{
public:
    Point();
    Point(int, int);
    Point(const Point& object);
    int getX() const;
    int getY() const;
    void setX(int);
    void setY(int);
    double calculate_area();
    void print() const;

private:
    int x;
    int y;
};

class Shape
{
public:
    Shape();
    double calculate_area();
    void print() const;

protected:
    double area;
};

class Circle : public Shape
{
public:
    Circle();
    Circle(const Point&, double);
    double getRadius() const;
    void setRadius(double);
    void calculate_area();
    void print() const;

private:
    double radius;
    Point center;
};

class RTriangle : public Shape
{
public:
    RTriangle();
    RTriangle(double, double);
    double hyp();
    void calculate_area();
    void print() const;

private:
    double side1;
    double side2;
};

inline double distance(Circle& other)
{
    return sqrt(pow(other.center.x, 2) + pow(other.center.y, 2));
}

#endif

//Implementation.cpp of what i think is important for you guys to see
Point::Point(int inX, int inY) // normal constructor
{
    x = inX;
    y = inY;
}

Point::Point(const Point &object) // copy constructor needed to use for center of circle
{
    x = object.x;
    y = object.y;
}
Circle::Circle(const Point& object, double inRad) // center is x & y... radius for circle
{
    center = object;
    radius = inRad;
}

My outside member function (inline double distance) isn't working. This is the first time I have tried doing this so I apologize if I do not word it well. I am essentially trying to use only the Circle class which inherits point center and point center is defined in the first class as x and y. Is it possible to do such a thing (specifically use x and y which is inside Point center)? I don't know if it's possible to access x and y through center.

Answer 1

Given a Point, functions not in Point can access its x and y members with the public getX() and getY() methods in your example.

However, Circle's center member is not public and has no public accessors. The most straightforward fix would add a public method

Point getCenter(); // or Point const &getCenter() if you like)

to Circle.