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 do Filter(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 use it as the encryption key

Second part of the question:

Create a subclass of the abstract filter class of programming challenge 5 (i.e example above) that double spaces a file: that is, it inserts a blank line between any two lines of the file