#include <iostream>
#include <string>
#include <algorithm>
#include <cctype>
/*
ROT13 is a simple substitution cipher that replaces a letter with the 13th letter
after it in the alphabet. Because the English alphabet has 26 letters (13 * 2),
applying ROT13 twice restores the original text (it is its own inverse).
*/
/**
* @brief Transforms a string using the ROT13 substitution cipher.
*
* @param text The input string (passed by value to support both lvalues and rvalues efficiently).
* @return std::string The processed ROT13 string.
*/
std::string rot13(std::string text) {
// std::transform applies a unary operation across the range [begin, end)
std::transform(text.begin(), text.end(), text.begin(), [](unsigned char c) {
if (std::isupper(c)) {
// Shift uppercase letters by 13, wrapping around with modulo 26
return static_cast<char>((c - 'A' + 13) % 26 + 'A');
}
if (std::islower(c)) {
// Shift lowercase letters by 13, wrapping around with modulo 26
return static_cast<char>((c - 'a' + 13) % 26 + 'a');
}
// Non-alphabetic characters (spaces, punctuation, digits) remain untouched
return static_cast<char>(c);
});
return text;
}
int main() {
// Modern C++ string management (safe, dynamic size, no manual buffer sizing)
std::string message = "Hello, World! 123";
std::cout << "Original: " << message << '\n';
// Apply ROT13 encryption
std::string encrypted = rot13(message);
std::cout << "ROT13: " << encrypted << '\n';
// ROT13 is its own inverse; applying it again decrypts the message
std::string decrypted = rot13(encrypted);
std::cout << "Decrypted: " << decrypted << '\n';
}
/*
run:
Original: Hello, World! 123
ROT13: Uryyb, Jbeyq! 123
Decrypted: Hello, World! 123
*/
