/*
 * Name: Ziying Hu & Xiaolong Zhou
 * Login: cs100vat & cs100vcc
 * Date: Aug 4, 2016
 * File: README
 */


1. d must be a constant lvalue reference, because a non-constant lvalue 
reference can only be assinged by lvalue. By adding const in front, d 
is a constant lvalue reference, thus it can be assigned by rvalue also. 

2.
a) The post-increment operator takes an int argument is actually a 
dummy parameter, which is used to distinguish pre-increment and
post-increment. Therefore, when using ++, it can know whether its 
pre-increment or post-increment.

b) The pre-increment operator increase the value of object and return 
a reference because the state of object operated and that returned is
the same. The post-increment, though, needs to return the old value 
of the object instead of the updated value object. Thus, a copy of the 
old object has been made before increment since the reference has been 
updated. If returning the reference, the updated value object would be
returned. Thus, a copy of the BSTIterator would return the old value 
object as required.