Simple Encryption program array

Question

Building a simple program that multiplies the ASCII value of chars in a string by 3 to encrypt and then divide by 3 to decrypt. So far I got the encryption part down but whenever I enter what the encryption gave and try to decrypt it doesn't work. I think it has something to do with the buffer stream but I could be wrong if anyone could help.

#include <iostream>

using namespace std;

int main()
{
    string message;
    int charValue;
    int counter;
    int encrypt;
    char choice;
    char quit = 'N';

    while (quit == 'N')
    {
        cout << "Enter E to encrypt or D to Decrypt\n";
        cin >> choice;
        toupper(choice);

        cout << "Enter text no spaces: ";
        cin >> message;

        int messagelen = message.length();
        string stringArray[255];

        if (choice == 'E')
        {
            for (counter = 0; counter < messagelen; counter++) //*3 to ascii val
            {
                stringArray[counter] = message[counter] * 3;
            }

            for (counter = 0; counter < messagelen; counter++)
            {
                cout << stringArray[counter];
            }
        }
        else
        {
            for (counter = 0; counter < messagelen; counter++) // divide 3 to ascii val
            {
                stringArray[counter] = message[counter] / 3;
            }

            for (counter = 0; counter < messagelen; counter++)
            {
                cout << stringArray[counter];
            }
        }

        cout << "\nY to go again N to quit";
        cin >> quit;
    }
    return 0;
}

Answer 1

This is a working implementation, although I agree with the other answer that you should use encrypt and decrypt functions. I found quite a few other bugs with your code working through it. You should enable all warnings with -Wall -Werror and fix them:

#include <iostream>
#include <vector>
#include <sstream>

int main()
{
  // removed some unused variables
  std::string message;
  size_t counter;
  char choice;
  char quit;
  // use vector of int instead of array of strings
  std::vector<int> encryptArray;

  // change to do while loop. Not particularly necessary, but I think
  // it makes more sense in this case. Your condition is broken. If the
  // user enters 'Y' at the end to go again, then the quit == 'N'
  // condition is false and the program terminates.
  do
  {
    std::cout << "Enter E to encrypt or D to Decrypt\n";
    std::cin >> choice;
    // toupper returns a value, you need to assign it to choice.
    // Not capturing the return value makes this a noop.
    choice = toupper(choice);

    if (choice == 'E')
    {
      std::cout << "Enter text no spaces: ";
      std::cin >> message;

      size_t messagelen = message.length();
      // initialize vector to input message length size
      encryptArray = std::vector<int>(messagelen);

      for (counter = 0; counter < messagelen; counter++) //*3 to ascii val
      {
        encryptArray[counter] = message[counter] * 3;
      }

      // Note, this 2nd loop is more work than you need, you could
      // simply put the std::cout line in the loop above below the
      // assignment
      for (counter = 0; counter < messagelen; counter++)
      {
        // added the separator just for clarity. You could also print
        // hex bytes
        std::cout << encryptArray[counter] << "|";
      }
    }
    else
    {
      // all the data we care about is in the vector now
      for (counter = 0; counter < encryptArray.size(); counter++) // divide 3 to ascii val
      {
        // you don't want to /3 what's in the message here, you want
        // to /3 the encrypted values, which are in the vector
        encryptArray[counter] = encryptArray[counter] / 3;
      }
      // plenty of ways to convert the vector to a string, this is not
      // a "modern" way.
      // Note, you could skip this loop entirely, and in the one
      // above, simply do ss << (char)(encryptArray[i] / 3);
      // Not necessary to write the data back to encryptArray first.
      std::stringstream ss;
      for (size_t i=0; i<encryptArray.size(); ++i)
      {
        ss << (char)encryptArray[i];
      }
      std::cout << "decrypted string: " << ss.str() << std::endl;
    }

    std::cout << "\nY to go again N to quit: ";
    std::cin >> quit;
  } while(quit != 'N'); // loop until quit == N

  return 0;
}

Finally, I removed using namespace std;, here's why

Things get squirrely working with stdin on godbolt, but here's a working demonstration, at least initially.