shift

    char shift(char& c){
        int alpbLen=strlen(Parse::alphabet);
        int pos=-1;
        while (++pos<alpbLen&&alphabet[pos]!=c);
        if (pos<alpbLen) { //if c is a member of alphabet
            pos=(pos+key+alpbLen)%alpbLen;
            return alphabet[pos];
        }
        else return c; //else return c without shift;
    }