To exchange objects, a temporary reference is required.

Code:

C temp = ob1;       //make temp point to

                    //where ob1 points

ob1 = ob2;          //make ob1 point to

                    //where ob2 points

ob2 = temp;         //make ob2 point

                    //to where temp points

                    //(i.e. where ob1

                    // originally pointed)