I have been trying to create a World class that can pass itself to an Object class so that the Object can react in a way to the World.
The only thing I can't figure out is how to include a class both ways.
I know it is possible.
Example:

class B
{
B();
~B();
update(G g);
};

class G
{
G();
~G();
B allTheBs[];
};


So you see I want both classes to be able to access each other.
Help please
?

You need to forward declare the class.
Note that this will not work if you have G as a member variable. (a pointer to G is fine, though)

BTW, just a technical note, I hope that your real code doesn't have the parameter to update() declared as "G g". This will cause a copy of the G object you pass in to be made for the parameter. You should instead have "G &g", or if you don't need to modify G, "const G &g" to ensure that no copy will be made. Making the copy will also mess up your original object if you have pointers that are freed in the destructor, but don't define a copy constructor.