-A stack is one form of data structure. Data is stored in stacks using the
FILO (First In Last Out) approach. At any particular instance, only the top
of the stack is accessible. Which means that in order to retrieve data that
is stored inside the stack, those on the upper part should be extracted first.
Storing data in a stack is also referred to as a PUSH, while data retrieval is
referred to as a POP