How do I call operator function to add two objects?

Question

Trying to develop operator == to compare two balls where two balls are considered equal if they have the same radius and operator > to compare two balls. To see if one ball has a bigger radius than another one, for let's say ball x is > than another ball y. += to add the volume of the right-side-operand to the volume of the left-side-operand. It is like to melt two metal balls to make one metal ball. The new ball's radius is cube root of (r1^3 + r2^3). Wish to use pow() function to calculate the cube value and cube root value. operator + to add the two balls together and return a new ball. The size of the new ball is the sum of the size of the two operands connected by the +.

In the main() function, couldn't add ball m(10) with ball n(20) to create another ball d, like d = m+n.

int main()
{
    //use ball
    ball x; float re;
    //radius of ball y is set to 10
    ball y(10);
    //asks for radius of x?
    cout << "Enter radius for ball x: ";
    cin >> re;
    //sets the radius of x
    x.set_radius(re);

    ball m(10);
    ball n(20);
    ball d;
    d = m + n;

    //cout << "The radius of ball d is " << m.;

    system("pause");
    return 0;
}

//ball.h
{
    class ball
    {
    public:
        //sets the intial raduis to 0
        ball() {
            radius = 0;
        }
        ball(float radii) {
            radius = radii;
        }
        float get_radius() {
            return radius;
        }
        void set_radius(float redly) {
            radius = redly;
        }
        bool operator == (ball x) {
            if (radius == x.radius)
                return true;
            else
                return false;
        }
        bool operator > (ball x) {
            if (radius > x.radius)
                return true;
            else
                return false;
        }
        bool operator += (ball x) {
            radius += x.radius;
        }
ball operator + (ball a, ball b) {
        ball d;
        d += a;
        d += b;
        return d;
    }
    private:
        float radius;
    };
}
#endif

Answer 1

If you are only looking for (x_volume/ y_volume)% and (x_surfacearea/y_surfacearea)%

I suggest doing :

float vol_over_y() {
    float v;
    v = ((radius * radius * radius)/(10*10*10));
    return v;
}
float sa_over_y() {
    float a;
    a = (radius * radius /(10*10));
    return a;
}    

because other constants like (4.0/3.0)* 3.14 in volume and 3.14 in surface area cancel out.

If in case y changes,

float vol_over_y(float y_rad) {
    float v;
    v = ((radius * radius * radius)/(y_rad*y_rad*y_rad));
    return v;
}
float sa_over_y(float y_rad) {
    float a;
    a = (radius * radius /(y_rad*y_rad));
    return a;
}    

Answer 2

You thought too much. It is simply a little tweak in your main logic:

ball x;
ball y(10);
// your code to construct x

cout << "The volume of x is " << ( x.volume() / y.volume() )<< "% of the volume of y."<< endl;

// similar for surface area, try it out yourself

---

If in case you really need to do it in a method(which is quite ridiculous imho), you should just pass the other ball in and calculate:

float volume_ratio_to(const ball& base) {
  return volume() / base.volume();
}

And your main logic become

cout << "The volume of x is " << x.volume_ratio_to(y) << "% of the volume of y."<< endl;

---

Edited for your updated question:

The reason why + operator does not work for you is because you didn't overloaded the operator right.

If you want it to be member of ball, the + operator should only takes one argument.

i.e. looks like:

class ball {
    //....
    ball operator + (ball another);
}

Or, don't make it member of ball:

// outside ball class
ball operator + (ball a, ball b) {....}

Refer to Overloaded Addition assignment operator in C++ for two /more than two objects? for more detailed description on how to overload addition operator.

There are quite a lot of other problems in your code too

• You should have passed balls to methods by reference instead of by value
• You should have considered adding const in various places
• You += logic is totally wrong. Pay attention to what you quoted:

  += to add the volume of the right-side-operand to the volume of the left-side-operand. It is like to melt two metal balls to make one metal ball. The new ball's radius is cube root of (r1^3 + r2^3)

Answer 3

//This helps

    int main()
    {  
        //use ball
        ball x; float re;
        ball y(10);
        cout << "Enter radius for ball x: " << endl;
        cin >> re;
        x.setl(re);

        cout << "The volume of x is " << (x.volume()/y.volume())*100 << "% 
of the volume of y."<< endl;
        cout << "The surfacearea of x box is " << 
(x.surface_area()/y.surface_area())*100 << "% of 
the surfacearea of y." << endl;

        system("pause");
        return 0;
    }

//ball.h
#pragma once
#ifndef Ball
#define Ball
namespace bsize
{
    class ball
    {
    public:
        ball(){
            radius = 0;
        }
        ball(float radii) {
            radius = radii;
        }
        float volume() {
            float v;
            v = ((4.0/3.0)* 3.14 * (radius * radius * radius));
            return v;
        }
        float surface_area() {
            float a;
            a = (4 * 3.14 * radius * radius);
            return a;
        }
        float get_radius(){
            return radius;
        }
        void set_radius(float redly) {
            radius = redly;
        }
    private:
        float radius;
    };
}
#endif