Step $1$: Inspect the UndoCommand abstract base class

The read$-$only UndoCommand.h file declares the UndoCommand abstract base class. The UndoCommand class represents a command object: an object that stores all needed information to execute an action at a later point in time. For this lab, a command object stores information to undo a grocery list change made by the user.

Step $2$: Inspect the incomplete GroceryList class

The GroceryList class is declared in GroceryList.h$.$ Two member variables are declared:

listItems: A vector of strings for list items

undoStack: A stack of UndoCommand pointers for undo commands

Note that the AddWithUndo$()$ member function is already implemented. The function adds a new item to the list and pushes a new RemoveLastCommand object onto the undo stack.