# Thread: Substitution Cipher Program Problem...

1. ## Substitution Cipher Program Problem...

<< split from 4 year old thread - read the rules http://cboard.cprogramming.com/cplus...m-problem.html >>

I am writing a simple substitution cipher also, though this is much more complex than mine. I built it so that it would follow a couple rules and generate it's own key, which it sent to a text file.

Here is what I wrote... not nearly as elegant, in my opinion. Works very simply, and correctly, though I think that the handling method is inefficient... it changes things to ascii, adds or subtracts to/from that ASCII value, then resets it as a (new) letter.

It does offer decryption capability, also... which, for the record, took MUCH longer to figure out than the initial encryption (weak though it is.)

Code:
```#include <iostream>
#include <string.h>
#include <algorithm>
#include <vector.h>
#include <string>
#include <time.h>
#include <fstream.h>

using namespace::std;

void encrypt (void);
void decrypt (void);

int main()
{
int choice;
while (choice != 3)
{
cout<<"What operation would you like to perform? \n";
cout<<"1 - Encrypt \n";
cout<<"2 - Decrypt \n";
cout<<"3 - Quit \n";
cin>>choice;
system("CLS");
switch (choice)
{
case 1:
encrypt();
break;
case 2:
decrypt();
break;
case 3:
break;
default: cout<<"Please enter a valid response. \n";
break;
}
}

return 0;
}

void encrypt ()
{
ofstream fout;
string plaintext;
string ciphertext;
string cipherletter;
string shift_string_1;
string shift_string_2;
char shift_letter;
signed int cipher_num;
signed int cipher_num_2;
signed int shifter;
signed int shift_num;
char letter;
cin>>plaintext;
signed int slength = plaintext.size();
signed int loops = 0;
signed int seed;
fout.open("key.txt");
fout.close();
fout.open("key.txt",ios::app);
fout<< "PLAINTEXT: " << plaintext << endl;
fout<<"KEY:";
while (loops < slength)
{
shifter = loops;
if (loops == 0)
{
shifter = slength;
}
if (loops % 2 < 1)
{
shifter = shifter * -1;
}
else
{
shifter = loops;
}
fout<<shifter;
cipher_num = int(plaintext[loops]);
cipher_num_2 = cipher_num + shifter;
letter = char(cipher_num_2);
cipherletter = letter;
ciphertext.append(cipherletter);
loops++;
}
fout<< endl <<"CIPHERTEXT: " << ciphertext <<endl;
fout.close();
system("PAUSE");
}

void decrypt ()
{
string encrypted;
string key;
cout<<"Please enter the encrypted text: \n";
cin>> encrypted;
system("CLS");
cout<<"Please enter the key, without signs: \n";
cin>>key;
signed short int shifter;
char letter;
char new_letter;
int cipher_num;
int new_num;
string deciphered;
string holder;
int slength;
int shifted_letter_num;
slength = encrypted.size();
int loops = 0;
int temp_num;
while (loops < slength)
{
temp_num = key[loops];
cipher_num = temp_num-48;
cout<<cipher_num;
if (loops % 2 < 1)
{
cipher_num = cipher_num * -1;
}
shifted_letter_num = int(encrypted[loops]);
cout<<"ASCII of the encrypted text: " << shifted_letter_num << endl;
new_num =shifted_letter_num - cipher_num;
letter = char(new_num);
holder = letter;
cout<<"Decrypted letter: " << holder << endl;
deciphered.append(holder);
loops++;
}
cout<<"Decrytpion done. Decrypted text: " << deciphered << endl;
system("PAUSE");
}```
I'd be interested in feedback on the process... the code is functional, but inefficient, I know... I am teaching myself, and this was an interest of mine that I decided to use to further my capabilities. I'm writing a new one that uses a more complex cipher system, multiple words, etc; it also uses the ASCII method, since it is what I know :P

2. Sorry about the bump... I was tired and missed the last post date.