Question

Lab #10 C++

Write a C++ program that reads text from a file and encrypts the file by adding an encryption factor (EF) to the ASCII value of each character. The encryption factor is 1 for the first line and increases by 1 for each line up to 4 and then starts over at 1. So, for the 4 th line the EF is 4, for the 5th line it is 1, for the 10th line it is 2. In General, for the Nth line, the encryption factor is (N -1) % 4 + 1.

If the seventh line of the input file is, “This is the seventh line of the file.” The seventh line of the encrypted file would have 3 added to each character. It would look like, “Wklv#lv#wkh#vhyhqwk#olqh#ri#wkh#iloh1”

See section 5.11 and sections 12.3-5 in Starting out with C++ for information on reading and writing to text files.

Your program should:

1. Read the provided plain.txt file one line at a time. Because this file has spaces, use getline (see section 3.8).

2. Change each character of the string by adding the encryption factor to it.

3. Write the encoded string to a second file, such as coded.txt

4. The encoded file should have the same structure as the original file, if the second line of the original file has 24 characters (including spaces) then there should be 24 characters on the second line of the encoded file (spaces will now be replaced by the characters !, ”, #, and $).

Hints:

1. In Visual Studio Express, put your plain.txt file in the project directory. The same folder that your C++ source (.cpp) file is in.

2. One of the challenges is to keep reading lines from the plain.txt file until the end. Program 12-8 is an example of how to do that.

plain.txt:

This is a sample input file for COSC 1436
assignment #10. Your program should encode this
file by adding 1 through 4 to the ASCII value of each
character in it. In your encoded file the first character should
be 'U'. The last character of the third line should be 'k'.
The encoded file should have the same number of lines as the input,
but will be unreadable. The last character of the last line will
be a '2'.

Answer 1

Whether you face any problem or need any modification then share with me in the comment section, I'll happy to help you.

Program:

// encryption.cpp

#include "stdafx.h"
#include<iostream>
#include<fstream>
#include<string>

using namespace std;

//main function
int main()
{
   ifstream fin;
   //open the input file
   fin.open("plain.txt");
   //check file exist or not
   if(!fin.is_open())
   {
       cerr<<"File not exist! " <<endl;
       return 1;
   }
   ofstream fout;
   //open the output file
   fout.open("coded.txt");

   string line;
   int encryption_factor, N = 1;

   //processing
   while(1)
   {
       //calculate encryption_factor
       encryption_factor = (N -1) % 4 + 1;
       //read a line from the file
       getline(fin, line, '\n');
       //check for end-of-file
       if(fin.eof()) break;
       //encrypt the line using encryption_factor
       for(int i=0; i<line.size(); i++)
       {
           line[i] = line[i] + encryption_factor;
       }
       //write to the file
       fout << line <<endl;
       //increase the line number
       N++;
   }
   //close the files
   fin.close();
   fout.close();

   return 0;
}

Output File: coded.txt

Uijt!jt!b!tbnqmf!joqvu!gjmf!gps!DPTD!2547
cuukipogpv"%320"[qwt"rtqitco"ujqwnf"gpeqfg"vjku
iloh#e|#dgglqj#4#wkurxjk#7#wr#wkh#DVFLL#ydoxh#ri#hdfk
glevegxiv$mr$mx2$Mr$}syv$irgshih$jmpi$xli$jmvwx$glevegxiv$wlsyph
cf!(V(/!Uif!mbtu!dibsbdufs!pg!uif!uijse!mjof!tipvme!cf!(l(/
Vjg"gpeqfgf"hkng"ujqwnf"jcxg"vjg"ucog"pwodgt"qh"nkpgu"cu"vjg"kprwv.
exw#zloo#eh#xquhdgdeoh1#Wkh#odvw#fkdudfwhu#ri#wkh#odvw#olqh#zloo
fi$e$+6+2