URGENT

C++ and Ubuntu Bash terminal

I only need Task 3 Please. Posted below contains task 2 code.

Introduction

The Caesar cipher is a substitution cipher where each letter in the original message (called the plaintext) is replaced with a letter corresponding to a certain number of letters up or down in the alphabet. The encrypted message (ciphertext) is not easily readable.

For example, here's the Caesar Cipher encryption of a message, using a left shift of 3.

Plaintext:

THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG

Ciphertext:

QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD

It is straightforward to recover the original message by using the opposite shift.

Task 1 (Weightage 50%)

You are asked to write a program that takes a shift value between +/- 26 and a plaintext message (no spaces) and returns the corresponding ciphertext. The program should also implement a decryption routine that reconstructs the original plaintext from the ciphertext.

Example usage

$ caesar Enter shift +/- 26: -3 Enter plaintext message (A-Z only, no spaces): THE ciphertext: QEB plaintext: THE

or

$ caesar Enter shift +/- 26: 1 Enter plaintext message (A-Z only, no spaces): ZZZ ciphertext: AAA plaintext: ZZZ

We assume that the user message only consists of uppercase English alphabet (A-Z).

Task 2 (Weightage 25%)

You are now to extend the above program to take as inputs files. The program should be able to read a file and encode or decode it as needed.

For the sake of simplicity, we assume that you only need to change letters [A-Z] in the file. You can safely ignore other letters in the file (i.e., keep those as is.)

Encrypting a file to cyphertext

Encrypt a file in.txt containing plaintext to a file out.txt containing ciphertext using shift . Flag -e here refers to encryption.

$ cf -e in.txt out.txt

Example

Consider f1.txt

HELLO WORLD THIS IS AMAZING WHY IS THIS SO AMAZING I HAVE NO IDEA 11231

After running the following command

$ ./cf -e 3 f1.txt f2.txt

File f2.txt looks like

KHOOR ZRUOG WKLV LV DPDCLQJ ZKB LV WKLV VR DPDCLQJ L KDYH QR LGHD 11231

Decrypting a file to plaintext

Decrypting a file in.txt containing ciphertext to a file out.txt containing plaintext using shift . Flag -d here refers to decryption.

$ cf -d in.txt out.txt 

Example

After running the following command

$ ./cf -d 3 f2.txt f3.txt

File f3.txt looks like

HELLO WORLD THIS IS AMAZING WHY IS THIS SO AMAZING I HAVE NO IDEA 11231

TASK 2 CODE

#include #include #include #include //only from A-Z

using namespace std; // get the ciphered text string encrypt(string str, int); // decrypt the cipher text string decrypt(string str, int);

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

if(argc != 5) { cout << "Usage: " << argv[0] << "

" << endl; return 1; }

bool encryptFlag = false; //check whethere we have to encrypt or decrypt if(strcmp(argv[1], "-e") == 0) encryptFlag = true; else encryptFlag = false;

//get the no. of shift int n = atoi(argv[2]);

ifstream infile(argv[3]); ofstream outfile(argv[4]);

if(infile.fail()) { cout << "ERROR: unable to open input file " << argv[3] << endl; return 1; }

if(outfile.fail()) { cout << "ERROR: unable to open output file " << argv[4] << endl; return 1; }

string line; string converted; while(getline(infile, line)) { if(encryptFlag) converted = encrypt(line, n); else converted = decrypt(line, n);

outfile << converted << endl; } cout << "Please check file " << argv[4] << endl; infile.close(); outfile.close();

return 0;

}

// get the ciphered text

string encrypt(string str, int n) { int i; for( i = 0 ; i < str.length() ; i++ ) { // to get ascii convert string to int int ascii = (int)str[i]; if(ascii >= 'A' && ascii <= 'Z') { ascii = ascii + n; if(ascii < 65) ascii = 91 - ( 65 - ascii ); else if(ascii > 90) ascii = 64 + (ascii - 90); // update the character with the ciphered text

str[i] = (char)ascii; } } return str;

}

// decrypt the cipher text

string decrypt(string str, int n) { int i; for( i = 0 ; i < str.length() ; i++ ) {

// get the ascii code

int ascii = (int)str[i]; if(ascii >= 'A' && ascii <= 'Z') {

ascii = ascii - n; if(ascii < 65) ascii = 91 - ( 65 - ascii ); else if(ascii > 90) ascii = 64 + (ascii - 90);

// update the character with the ciphered text str[i] = (char)ascii; }

}

return str;

}

COMPLETE TASK 3 THANK YOU

Task 3 (Weightage 25%)

Now change the code such that the following commands work as intended. Notice here we are using IO redirection to specify input and output files/streams.

Encryption

$ ./cf -e 3 < f1.txt > f2.txt

and

$ cat f1.txt | ./cf -e 3 > f2.txt

Decryption

$ ./cf -d 3 < f3.txt > f3.txt

and

$ cat f2.txt | ./cf -d 3 > f3.txt