//
// decrypt1.cpp
// CSC 215
// John Rogers
//
// This program decrypts the input
// in a text file selected by the
// user and places the output in
// a text file selected by the user.
// It does this by performing 
// character input and output.
//

#include <iostream.h>
#include <fstream.h>
#include <stdlib.h>
#include <ctype.h>

void openFiles(ifstream& inputFile, 
               ofstream& outputFile);
char decrypt(char encryptedChar, char key);

int main()
{
  ifstream inputFile;
  ofstream outputFile;
  char encryptedChar, decryptedChar, key;

  openFiles(inputFile, outputFile);
  cout << "Please enter the key character: ";
  cin >> key;
  
  inputFile.get(encryptedChar);
  while (! inputFile.eof()) {
    decryptedChar = decrypt(encryptedChar, key);
    outputFile.put(decryptedChar);
    inputFile.get(encryptedChar);
  }
  
  inputFile.close();
  outputFile.close();
  
  return 0;
}
  
//
//
// This function prompts the user for and opens 
// two files: one for input and one for output.
// The first is connected to an input file stream
// object and the second to an output file stream
// object, both of which are passed as call-by-
// reference parameters.
//
void openFiles(ifstream& inputFile, ofstream& outputFile)
{
  char inputFileName[50], outputFileName[50];
  
  do {
    cout << "Please enter the name of the input file: ";
    cin >> inputFileName;
    inputFile.open(inputFileName);
    if (inputFile.fail()) {
      cout << "Cannot open the file: " << inputFileName << endl;
    }
  } while (inputFile.fail());

  do {
    cout << "Please enter the name of the output file: ";
    cin >> outputFileName;
    outputFile.open(outputFileName);
    if (outputFile.fail()) {
      cout << "Cannot open the file: " << outputFileName << endl;
    }
  } while (outputFile.fail());

  return;
}

//
//
// This function uses an exclusive-or
// to decrypt a character.  Note that
// _all_ characters get decrypted.
//

char decrypt(char encryptedChar, char key)
{
  char decryptedChar;

  decryptedChar = encryptedChar ^ key;
  return decryptedChar;
}