How to find volume of cylinder using friend function with 2 classes?

CODE

How to find volume of cylinder using friend function with 2 classes?

//Write a program to find volume of cylinder using friend function with 2 classes…

#include<iostream>

using namespace std;

class data2;

class data1

{

    float r;

public:

    void input()

    {

        cout<<"\n enter r:";

        cin>>r;

    }

    friend void volume(data1 obj1,data2 obj2);

};

class data2

{

    float h;

public:

    void input()

    {

        cout<<"\n enter h:";

        cin>>h;

    }

    friend void volume(data1 obj1,data2 obj2);

};

void volume(data1 obj1,data2 obj2)

{

    float v=3.14*obj1.r*obj1.r*obj2.h;

    cout<<"\n volume="<<v;

}

int main()

{

    data1 obj1;

    data2 obj2;

    obj1.input();

    obj2.input();

    volume(obj1,obj2);

}

Output:

enter r:3

 enter h:5

 volume=141.3