Function of one class friend of another class

Question

I have two classes X and Y.

Y has a private member mark, X has a function getmark().
I declared getmark() as a friend of Y.

Now, how do I access the private member mark of Y using the friend function?

This is the code I have so far

#include<iostream>

using namespace std;

class X
{
    public:
    int getmark();
};

class Y
{
    int mark;
    public:
    friend int X::getmark();
};

int main()
{

}

Answer 1

#include<iostream>

using namespace std;   

class Y; //forward declaration of class Y
class X
{
    public:
    int getmark(Y);
};

class Y
{   
    int mark;
    public:
    friend int X::getmark(Y);
};

int X::getmark(Y obj){
    cin>>obj.mark;
}

int main()
{
  X a;  
  Y b;
  a.getmark(b);
}

At first, when the object a (class X) is created, a forward declaration of class Y is necessary in order to declare the Y argument to X::getmark().

Creating object b (class Y) wont be a problem as the compiler knows class X exists (for the friend function).

Then, simply call the function getmark() through the object a.

Note: It is necessary to declare the function getmark() after the declaration of class Y, or else compiler will consider the class Y as an incomplete type.