ICS4U Encryption Assignment

encryption-assignment.cpp

/*

    Curtis Davies - ICS4U Encryption Assignment
    Thursday, 1 February, 2018

    This program takes a data file "encode.dat" as input and encrypts any
    alphabetical characters after the first line,using the first line as a key.
    The encrypted text is outputted to the screen afterwards.

*/


#include <iostream>
#include <fstream>
#include <cstring>

int main(int argc, char *argv[]) {

    // Declare variables
    char key[64], feed[64], toenc, enchar;
    int keylen = 0, kid = -1;

    // Whitespace to make the program look pretty!
    std::cout << std::endl;

    // Check if data file exists, throw error if not found.
    std::ifstream fin("encode.dat");
    if (!fin) {
        std::cout << "encode.dat not found" << std::endl;
        return 1;
    } else {
        std::cout << "encode.dat found! Encrypting string..." << std::endl << std::endl;
    }

    // Read key into memory and save its length for processing
    fin >> key;
    keylen = std::strlen(key) - 1;

    // Print the key to the screen and prepare the console for the encrypted string
    std::cout << "Key: " << key << std::endl << std::endl << "Output: ";

    // Keep feeding text into the encryptor until the end of the file is reached
    // 'feed' represents the current word
    while (fin >> feed) {

        // Repeat this loop for each letter in the current word
        for (int i = 0; i < strlen(feed); i++) {

            // If the character is not an uppercase letter, skip it
            if (feed[i] > 'Z' || feed[i] < 'A') continue;

            // Proceed to the next letter in the key. When the end of the key is reached, loop to the beginning again
            kid++;
            if (kid > keylen) {
                kid = 0;
            }

            // If the character of the key is not an uppercase letter, skip it
            if (key[kid] > 'Z' || key[kid] < 'A') continue;

            // If the code exceeds Z, loop back to ASCII code 65 (A)
            if ((key[kid] - 65) + feed[i] > 'Z') {
                enchar = key[kid] - 91 + feed[i];
            } else {
                enchar = key[kid] - 65 + feed[i];
            }

            // Print the encrypted character to the screen
            std::cout << enchar;
        }
    }

    // After the text is outputted, print an endline
    std::cout << std::endl;

    // Program has finished properly, return 0
    return 0;
}