Program enkripsi sederhana C++

#include <iostream>
#include <string>

std::string encrypt(std::string message, int key) {
    std::string encryptedMessage = "";
    for (int i = 0; i < message.length(); i++) {
        char c = message[i];
        if (isalpha(c)) {
            if (isupper(c)) {
                encryptedMessage += char(int(c + key - 65) % 26 + 65);
            } else {
                encryptedMessage += char(int(c + key - 97) % 26 + 97);
            }
        } else {
            encryptedMessage += c;
        }
    }
    return encryptedMessage;
}

int main() {
    std::string message;
    int key;

    std::cout << "Masukkan pesan yang ingin dienkripsi: ";
    std::getline(std::cin, message);

    std::cout << "Masukkan kunci enkripsi: ";
    std::cin >> key;

    std::string encryptedMessage = encrypt(message, key);

    std::cout << "Pesan terenkripsi: " << encryptedMessage << std::endl;

    return 0;
}