Answered Essay: How would you create a C++ program to do encoding and decoding of messages using the Vignere cipher usin

Given below is the code for the question. Please do rate the answer if it helped. Thank you.

#include <iostream>
#include <cctype>
using namespace std;
class VignereCipher
{
string key;

public:
VignereCipher(string key);
string encode(string message);
string decode(string message);
};

VignereCipher::VignereCipher(string key)
{
this->key = “”;
for(int i = 0; i < key.size(); i++)
this->key += toupper(key[i]);

}

string VignereCipher::encode(string msg)
{
int k = 0;
string encoded = “”;
int M, C;
char ch;
for(int i = 0; i < msg.size(); i++)
{
M = toupper(msg[i]) – ‘A’;
if(M >= 0 && M < 26)
{
C = key[k] – ‘A’;
ch = ‘A’ + ( M + C) % 26;
encoded += ch;
k = (k + 1) % key.length();
}
}
return encoded;
}

string VignereCipher::decode(string msg)
{
int k = 0;
string decoded = “”;
int M, C;
char ch;
for(int i = 0; i < msg.size(); i++)
{
M = toupper(msg[i]) – ‘A’;
if(M >= 0 && M < 26)
{
C = key[k] – ‘A’;
ch = ‘A’ + ( M – C + 26) % 26;
decoded += ch;
k = (k + 1) % key.length();
}
}
return decoded;
}

int main(int argc, char *argv[])
{
if(argc != 3)
{
cout << “usage: ” << argv[0] << ” <-e or -d> <key>” << endl;
return 1;
}
string key = string(argv[2]);
VignereCipher vc(key);
string mode = string(argv[1]);
string msg;
cout << “Enter the message: “;
getline(cin, msg );

if(mode == “-e”)
cout << “encoded message: ” << vc.encode(msg) << endl;
else if(mode == “-d”)
cout << “decoded message: ” << vc.decode(msg) << endl;
else
cout << “mode can be -d or -e only.” << endl;

}

output

./a.out -e CSELEVEN
Enter the message: This is a test
encoded message: VZMDMNEGGKX

========

./a.out -d CSELEVEN
Enter the message: VZMDMNEGGKX
decoded message: THISISATEST