Overloading Volume Bola

#include <cstdlib>

#include <iostream>

using namespace std;

class bilangan{

      friend istream& operator>>(istream&, bilangan&);

      friend ostream& operator<<(ostream&, bilangan&);

public :

       bilangan();

       void proses(int x);

private :

        double r,V;

        };

bilangan::bilangan(){

                     cout<<"menghitung volume bola"<<endl;

                     }

void bilangan::proses(int x){

     V=(4/3)*(3.14)*r*r*r;

     }

istream& operator>>(istream& in, bilangan& x){

         cout<<"masukkan jari-jari=";

         in>>x.r;

         }

ostream& operator<<(ostream& out, bilangan& z){

         out<<"volume=";

         out<<z.V;

         }

        

int main(int argc, char *argv[])

{

    int z;

    bilangan a;

    cin>>a;

    a.proses(z);

    cout<<a<<endl;  

    system("PAUSE");

    return EXIT_SUCCESS;

}

Jika diinputkan 3, maka hasilnya: