Thread: class prototypes

Why doesn't this compile:

[edit]sorry got slightly ahead of myself

Code:

class b;

class a
{
public:
	int m_a;

	a ()
	{
	};
	a (b *bb)
	{
		m_a = bb->m_b;
	};
};

class b
{
public:
	int m_b;

	b ()
	{
	};
	b (a *aa)
	{
		m_b = aa->m_a;
	};
};