#include <iostream>
    using namespace std;
    class BoxExample
    {
        double W;
        public:
        friend void printW(BoxExample box );
        void setW( double width );
    };
    void BoxExample::setW( double width )
    {
        W = width;
    }
    void printW(BoxExample box )
    {
        box.W = box.W * 3;
        cout << "Width of box : " << box.W << endl;
    }
    int main( )
    {
        BoxExample box;
        box.setW(15.0);
        printW( box );
        return 0;
   }