void encode(char *s, char *enct){
  for (; *s != '\0'; s++) {
    *s = *(enct + *s - 'A');
  }
}

void decode(char *s, char *enct){
  int i; 
  char *p;
  for (; *s != '\0'; s++) {
    for (p = enct, i = 0; *p != *s; p++){
       i++;}
    *s = 'A' + i;
  }
}
   

int main() {
  char s[25] = "DEAF";
  char enct[27] = "XYZABCUVDEFRSTGHIOPQJKLMNO\0";
  printf("original string: %s\n",s);
  encode(s,enct);
  printf("after encoding: %s\n",s);
  decode(s,enct);
  printf("after decoding: %s\n",s);
}