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.

Answer in c++ please