C / C++ / MFC

struct BB;

struct AA
{
    struct BB *bb;
    int a;
};
struct BB
{
    struct AA *aa;
    int b;
};

main ()
{
    AA a;
    BB b;

    a.bb->b = 1;   // Will compile, but will crash horribly, because a.bb doesn't have any useful value in it.
}

AA a;
BB b;

a.bb = &b;
b.aa = &a;

a.bb->b = 1;
b.aa->a = 3;

Iain Clarke wrote:

I'd go back to your C book

struct AA a;
struct BB b;
a.bb = &b;
b.aa = &a;
a.bb->b = 1; //Just fine!
b.aa->a = 3; //Just fine! 

Iain Clarke wrote:

Though you could have worked that out for yourself...

Dennis L wrote:

My teacher has told me this project is going to be published with no fee in the internet.

Class A
{
    Class B
    {
        Class A
        {
            Class B
            {
                Class A
                {
                    .
                    . // etc...
                    .
                }
            }
        }
    }
}

// No need to include "class B"'s header.
 
class B; // Forward reference.
 
class A
{
...
private:
    ClassB &classB; // A reference to class B, not an instance.
};

// No need to include "class A"'s header.
 
class A; // Forward reference.
 
class B
{
...
private:
    ClassA &classA; // A reference to class A, not an instance.
};