prob_0.txt

The problem for this exercise is a listbox controller in a graphical user interface. You have to write code which accepts a list of items for the listbox and changes the currently selected item in the list. 

When the listbox is initialized, the current selection is the first element in the list.  Two operations: arrowUp and arrowDown allow you to change the position of the current selection.  If you arrowUp when the first element of the list is selected, it is a no-op.  Likewise, it is  a no-op if you arrowDown when the last element of the list is selected.  

If the controller is given an empty list, there is no currently selected item.

In later iterations, we will expand this behavior to make it more interesting.