Write a C++ program performing the rot13 cipher, The code should
perform like this:
The user should be able to input any letter or words, or even
sentences where once they have inputted the particular word, each
letter goes 13 letters ahead, so an 'A' becomes an 'N', a 'C'
becomes 'P', and so on. If rot13 cipher is tested a second time,
the original plantext should be restored: 'P' becomes 'C', 'N'
becomes 'A'. The 13 letters go in...