C++ Program to Implement Affine Cipher

Code:

#include    iostream
#include    string.h
#include    stdlib.h
using namespace std;
string encryptionMessage(string Msg)
{
    string CTxt = "";
    int a = 3;
    int b = 6;
    for (int i = 0; i < Msg.length(); i++)
    {
        CTxt = CTxt + (char) ((((a * Msg[i]) + b) % 26) + 65);
    }
    return CTxt;
}

string decryptionMessage(string CTxt)
{
    string Msg = "";
    int a = 3;
    int b = 6;
    int a_inv = 0;
    int flag = 0;
    for (int i = 0; i < 26; i++)
    {
        flag = (a * i) % 26;
        if (flag == 1)
        {
            a_inv = i;
        }
    }
    for (int i = 0; i < CTxt.length(); i++)
    {
        Msg = Msg + (char) (((a_inv * ((CTxt[i] - b)) % 26)) + 65);
    }
    return Msg;
}
int main(int argc, char **argv)
{
    cout << "Enter the message: ";
    string message;
    cin >> message;
    cout << "Message is :" << message;
    cout << "\nEncrypted Message is : " << encryptionMessage(message);

    cout << "\nDecrypted Message is: " << decryptionMessage(
            encryptionMessage(message));
}


Output:

Enter the message: SANFOUNDRY
Message is :SANFOUNDRY
Encrypted Message is : VTGIJBGCSN
Decrypted Message is: SANFOUNDRY
------------------
(program exited with code: 0)
Press return to continue


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