Chegg Question

chegg_1491721626696.cpp

/**
 * "Sun Apr 09 2017 12:36:54 GMT+0530 (IST)"
 * Design a file filter package.
 *
 * 1) A file filter reads an input file, transforms it in some way, and writes the result to an output file.
 * You are tasked to write an abstract Filter class that defines a pure virtual function char transform
 * (char ch) for transforming a single character . 
 *
 * 2) The Filter class should have member variables to hold the input and output streams; it also should
 * have a default constructor that initializes the input/output streams to cin/cout respectively as well
 * as a constructor that accepts initialized input/output file streams and uses them to initialize the 
 * Filter object . 
 *
 * 3) The Filter class will also have a member function void doFilter() that will use the 
 * char transform(char ch) virtual function to do the filtering. Using your Filter class , create one 
 * derived class that performs encryption using ROT13 algorithm (explained below), another that 
 * transforms a file to all uppercase, and another that creates an unchanged copy of the original file.
 * Write the main function that would open the file named "input.txt" and then use the three file filters
 * to create 3 new files: input.txt_copy for the copy filter, input.txt_encr for the encryption filter,
 * and input.txt_upper for the uppercase filter. 
 *
 * ROT13: ------ ROT13 stands for "rotate by 13 places" and is a simple cipher based on substitution. 
 * To encrypt or decrypt using ROT13, each letter of the alphabet is replaced by a letter that is 13 
 * places further along the alphabet. For example, A becomes N and M becomes Z; similarly, N becomes 
 * A and Z becomes M. Only letters (both upper and lowercase) are affected by this algorithm; i.e.
 * spaces, punctuation marks, digits and special characters are unchanged.
 */