Vigenère cipher

Vigenère cipher is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Implement a Vigenère cypher, both encryption and decryption. The program should handle keys and text of unequal length, and should capitalize everything and discard non-alphabetic characters. (If your program handles non-alphabetic characters in another way, make a note of it.)

See also:

• [Vigen%C3%A8re Cipher/Cryptanalysis]

C++

<lang cpp>#include <iostream>

1. include <string>

using namespace std;

class Vigenere { public:

 string key;

 Vigenere(string key)
 {
   for(int i = 0; i < key.size(); ++i)
   {
     if(key[i] >= 'A' && key[i] <= 'Z')
       this->key += key[i];
     else if(key[i] >= 'a' && key[i] <= 'z')
       this->key += key[i] + 'A' - 'a';
   }
 }

 string encrypt(string text)
 {
   string out;

   for(int i = 0, j = 0; i < text.length(); ++i)
   {
     char c = text[i];
     
     if(c >= 'a' && c <= 'z')
       c += 'A' - 'a';
     else if(c < 'A' || c > 'Z')
       continue;

     out += (c + key[j] - 2*'A') % 26 + 'A'; 
     j = (j + 1) % key.length();
   }

   return out;
 }

 string decrypt(string text)
 {
   string out;

   for(int i = 0, j = 0; i < text.length(); ++i)
   {
     char c = text[i];
     
     if(c >= 'a' && c <= 'z')
       c += 'A' - 'a';
     else if(c < 'A' || c > 'Z')
       continue;

     out += (c - key[j] + 26) % 26 + 'A'; 
     j = (j + 1) % key.length();
   }

   return out;
 }

};

int main() {

 Vigenere cipher("VIGENERECIPHER");

 string original = "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!";
 string encrypted = cipher.encrypt(original);
 string decrypted = cipher.decrypt(encrypted);

 cout << original << endl;
 cout << "Encrypted: " << encrypted << endl;
 cout << "Decrypted: " << decrypted << endl;

}</lang>

Output:

Beware the Jabberwock, my son! The jaws that bite, the claws that catch!
Encrypted: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY
Decrypted: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH