Answer Happy

A file filter reads an input file, transforms it in some way,
and writes the results to an output file. Write an abstract file
filter class that defines a pure virtual function for transforming
a character. Create one subclass of your file filter class that
performs encryption, another that transforms a file to all
uppercase, and another that creates an unchanged copy of the
original file.
The class should have a member function
void doFilter(ifstream &in, ofstream &out)
that is called to perform the actual filtering. The member
function for transforming a single character should have the
prototype
char transform(char ch)
The encryption class should have a constructor that takes an
integer as an argument and uses it as the encryption key.
Be sure to include comments throughout your code where
appropriate.