Question

In this assignment you will write a program that encrypts a text file.  You will use the following encryption scheme.

1. Ask the user for the name of the original file.
2. Ask the user for the name of the output file.
3. Ask the user for the encryption key, n.
4. Read n² characters from the file into the n rows and n columns of a 2-dimensional array.
5. Transpose the array.  (Exchange the rows and columns.)
6. Write the characters from the array to an output file.
7. Repeat steps 4 – 6 until the entire input file has been read.

This same program can be used to decrypt a file that has been encrypted in this way.

Your program should have functions for performing each of the following tasks.

1. Reading the characters from the file into the array.  This function should be passed the file stream, the array and the key.
2. Transposing the array.  This function should be passed the array and the key.  (Make sure you include this function as this is an exercise in parameter passing.)
3. Writing the characters from the array to the file.  This function should be passed the file stream, the array and the key.

Your main function should get the filenames, open the files, get the key, dynamically allocate the memory for the array, and close the files.

Your program should also:

Give detailed directions and warnings to the user.

• Be readable with appropriate documentation and formatting.  Be sure to include carefully written pre and post conditions for each of your functions.

Answer 1

Code is as following:

#include <iostream>
#include <fstream>
#include <bits/stdc++.h>

using namespace std;
//transpose the array
void transpose(char *A, char *B, int n){
  int i, j; 
    for (i = 0; i < n; i++) 
        for (j = 0; j < n; j++) 
            *((B+i*n)+j) = *((A+j*n)+i); 
}

//read the characters to the array
void readCharsToArray(ifstream &fin,char *arr,int n){
  char ch;
  for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
          if(fin >> noskipws >> ch)
            *(arr+(i*n)+j) = ch;
          else
            break;
        }
  }
}

int main() {
  int n = 0; string inFile, outFile;
  cout<<"Enter input file name: ";
  cin>>inFile;
  cout<<"Enter output file name: ";
  cin>>outFile;
  while(n<1){
    cout<<"Enter key('n'):"<<endl;
    cin>>n;
    if(n<1)
      cout<<"Enter valid key!!"<<endl;
  }

  //construct n-by-n matrix
  char arr[n][n];
  char temp[n][n];
  memset(arr,'$',sizeof(arr));


  //open input file
  ifstream fin(inFile);

  ofstream fout;
  //first open output file to format all content, if it already exists
  fout.open(outFile);
  fout.close();

  //open output file in append mode
  fout.open(outFile,ios::app);

  while(fin){
    readCharsToArray(fin,arr[0],n);
    transpose(arr[0],temp[0],n);
    for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
          if(temp[i][j]!='$')
            fout<<temp[i][j];
        }
    }
    memset(arr,'$',sizeof(arr));
  }
  fin.close();
  fout.close();
  
}

Sample output after running program on file "input.txt"

Following Sample output is shown on the following input.txt file:-

Output of file encrypt.txt is as following:-

Output of second run on file "encrypt.txt" is as following:

Output of decrypt.txt file is as following:-

Note - If any doubt/queries, do ask in comment section