cVizhenerSimple

#include <stdio.h>


const int alphaLength = 26;

char* vizhiner(char* str, const char* key, int mode)
{
    char* origStr = str;
    size_t keyLength = strlen(key);
    int keyPos = 0;
    while (*str)
    {
        if (mode)
        {
            *str++ = ('A' + (*str + *(key + keyPos)) % alphaLength);
        }
        else
        {
            *str++ = ('A' + (*str + alphaLength - *(key + keyPos)) % alphaLength);
        }

   //     *str++ = ('A' + (*str + (mode ? *(key + keyPos++) : alphaLength - *(key + keyPos++))) % alphaLength);
        ++keyPos;
        keyPos %= keyLength;
    }
    return origStr;
}


int main()
{//

    char str[] = { "ATTACKATDAWN" };
    char key[] = { "LEMON" };
    printf("Original:\t%s\n", str);
    printf("Encoded:\t%s\n", vizhiner(str, key, 1));
    printf("Decoded:\t%s\n", vizhiner(str, key, 0));

    return 0;
}