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$13\mathrm{.}7$ LAB: Iterable $2-3-4$ tree

In this lab, the Tree$234$ class is extended to support iteration with a range$-$based for loop. Such support is provided via the implementation of an iterator that can iterate through the tree's keys in ascending order.

An iterator is an object that maintains a pointer to a specific element in a collection and can move to the next element. Ex: A Tree$234$ iterator points to the tree's minimum key upon construction. The iterator can then move to the second to minimum key, then the third to minimum, and so on$.$ After moving past the tree's last key, the iterator can move no further.

Overview of iterable objects in $C++$

This lab requires implementation of a simplified iterator that:

implements the dereference operator $(**)$ to return the key that the iterator currently points to$,$

implements the pre$-$increment operator $(++)$ to advance to the next key,

supports copy construction and copy assignment, and

supports equality and inequality comparison.

Range$-$based for loops work on any class that implements the begin$()$ and end$0$ member functions such that each returns an iterator. So Tree$234$ implements begin $0$ and end $0.$ Tree$234\text{'}$s begin $0$ member function returns an instance of Tree$234$lterator object representing the inclusive starting point of iteration: the tree's minimum key. Tree$234\text{'}$s end $0$ member function returns an instance of Tree$234$lterator object representing the exclusive ending point of iteration: one beyond the tree's maximum key.

Step $1$: Inspect the Node$234.$h file

Inspect the Node$234.$h file. Access Node$234.$h by clicking on the orange arrow next to main.cpp at the top of the coding window. Node$234.$ his read only and has a complete implementation of a Node$234$ class for a $2-3-4$ tree node. Member variables are protected and so must be accessed through the provided getter and setter functions.

Step $2$: Inspect the Tree$234$Iterator.h file

Inspect the Tree$234$lterator.h file. The Tree$234$lterator class is declared, but required member functions are not implemented. The