DocumentedPolybiusSquareCipher.cpp

namespace PolybiusCipher {
//Cipher and decipher maps, which will be initialised depending on the key
    map<char, string> cipherMap;
    map<string, char> decipherMap;

/**
 * Map initialising function using the key sent as a parameter.
 * cipher is a boolen parameter to check if this map is a cipherMap or a decipherMap
 * It loops over every position possible in a 5x5 table (00, 01, etc.) and uses this equation (j + i * 5 + 'a')
 * to determine the character we should map this index to.
 * In the case cipher is true, we insert the characterIndex we calculated mapped to the row+column string value
 * For eg. 'a' : "55" in the case that the row is 5, and column is 5 (first digit in the key is 5).
 * In the case the cipher is false, each row+column string value is mapped to the character.
 * For eg. "55" : "a" in the case that the row is 5, and column is 5 (first digit in the key is 5).
*/
    void initMap(string key, bool cipher) {
        for (int i = 0; i < 5; ++i) {
            for (int j = 0; j < 5; ++j) {
                string row = to_string(key[i] - '0'), column = to_string(key[j] - '0');
                int charIndex = j + i * 5 + 'a';
                if (cipher)
                    cipherMap.insert({(char) (charIndex > 'i' ? charIndex + 1 : charIndex), row + column});
                else
                    decipherMap.insert({row + column, (char) (charIndex > 'i' ? charIndex + 1 : charIndex)});
            }
        }
    }

/**
 * Function that handles taking the input and deciphering the message.
 * It takes a string from a user, and a key, and calls initMap function with
 * the key and cipher = false. Then it loops over the string and checks for every
 * two consecutive digits and checks for their representation(value) in the decipherMap
 * and adds it to decipheredMessage. If a space is found, it adds the space to the
 * decipheredMessage string and adds one to the iterator value i.
 */
    void decipherMessage() {
        string userInput, decipheredMessage, key, decipheredAlpha;
        cout << "Enter a message you would like to decipher:" << endl;

        getline(cin, userInput);

        cout << "Cipher key (5 numbers, eg: 51432):" << endl;
        getline(cin, key);
        while (key.size() != 5 || to_string(stoi(key)) != key) {
            cout << "Cipher key must be 5 digits next to each other.\nCipher key (5 numbers, eg: 51432):" << endl;
            getline(cin, key);
        }

        initMap(key, false);

        for (int i = 0; i < userInput.size(); i += 2) {
            string currTwoDigits = userInput.substr(i, 2);
            if (isdigit(currTwoDigits[0]) && isdigit(currTwoDigits[1]))
                decipheredMessage += decipherMap[currTwoDigits];
            else
                decipheredMessage += currTwoDigits;
            if (userInput[i + 2] == ' ') {
                decipheredMessage += ' ';
                i++;
            }
        }

        cout << "The deciphered message is: " + decipheredMessage << endl;
    }

/**
 * Function that handles taking the input and ciphering the message.
 * It takes a string from a user, and a key, and calls initMap function with
 * the key and cipher = true. Then it loops over the string and checks for every
 * letter, and checks for their representation(value) in the cipherMap and adds it to cipheredMessage.
 * If the letter is found, it adds value found in the map, else, it adds the character itself.
 */
    void cipherMessage() {
        string userInput, cipheredMessage, key;
        cout << "Enter a message you would like to cipher:" << endl;

        getline(cin, userInput);

        cout << "Cipher key (5 numbers, eg: 51432):" << endl;
        getline(cin, key);
        while (key.size() != 5 || to_string(stoi(key)) != key) {
            cout << "Cipher key must be 5 digits next to each other.\nCipher key (5 numbers, eg: 51432):" << endl;
            getline(cin, key);
        }

        initMap(key, true);

        for (char i: userInput)
            if (isalpha(i))
                cipheredMessage += cipherMap[tolower(i == 'j' ? 'i' : i)];
            else
                cipheredMessage += i;

        cout << "Ciphered message: " + cipheredMessage << endl;
    }
}