Invariant of the Bag ADT (ctd.)
The Invariant for our first implementation of the Bag ADT is:
The number of items in the Bag is stored in the member variable used;
For an empty bag, we do not care about what is stored in the array data; for a non-empty bag, the elements of the bag are stored in data[0] to data[used-1] and we do not care about the rest of data.