Friend Function Program in C++

/*A friend function allows you to generate more efficient

code. The following program illustrates this concept:*/

#include <iostream.h>

#include <conio.h>

const int IDLE = 0;

const int INUSE = 1;

class C2; // forward declaration

class C1 {

int status; // IDLE if off, INUSE if on screen

// ...

public:

void set_status(int state);

friend int idle(C1 a, C2 b);

};