/* Code for exercise 7.9. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*/#include <iostream.h>int main(int argc, char *argv[]) {   std::cerr << "Note: This program tends to produce non-printable output.\n"                "      It is therefore recommended to redirect cin and cout\n"                "      from and to files. On many systems this can be done\n"                "      with a command like: \n"                "         encode key <input_file >output_file\n";   char const *key = (argc>=2)? argv[1]: "";   size_t key_length = (argc>=2)? std::strlen(key): 1;   char ch;   for (std::size_t k = 0; std::cin.get(ch); k = (k+1)%key_length)      std::cout.put(ch^key[k]);   return 0;}