Write a C++ preorder iterator to supply tree nodes to the loop in Example 6.69. You will need to know (or learn) how to use pointers, references, inner classes, and operator overloading in C++. For the sake of (relative) simplicity, you may assume that the data in a tree node is always an int; this will save you the need to use generics. You may want to use the stack abstraction from the C++ standard library.