How to find volume of cylinder using friend class ?

CODE

How to find volume of cylinder using friend class ?

//Write a program to find volume of cylinder using friend class…

include<iostream>

using namespace std;

class data

{

    float r,h;

public:

    void input()

    {

        cout<<"\n enter r and h:";

        cin>>r>>h;

    }

    friend class pro;

};

class pro

{

    public:

    void volume(data obj)

    {

        float v=obj.r*obj.h*3.14*obj.r;

        cout<<"\n volume="<<v;

    }

};

int main()

{

    data obj;

    obj.input();

    pro p;

    p.volume(obj);

}

Output:

enter r and h:5

7

 volume=549.5