Stream Processing:

    Note how we use the istream and ostream types for generic
    stream arguments.  This will allow both file streams and
    the console streams to be passed through the same function
    argument.  (This power is thanks to inheritance, which we
    will cover later this semester.)

    Stream arguments are always pass-by-reference since no
    matter what you are doing to a stream, you change either
    the memory version (object/buffer) or the physical version
    (screen/file).

    Also note the default values on the stream arguments.
    This is possible because cin and cout are global variables.
    Normally reference arguments cannot have defaults because
    there is no-where to refer which always exists.  Since
    cin and cout are always available, we can always refer to
    them.