/* Convert the string n to a decimal number in base and return it.
   Assume that input string is without errors */
int to_decimal_number(char *n, int base){
  int ciffer_number, res = 0;
  char *ciffer_ptr = &n[0], ciffer = *ciffer_ptr;

  do {
    if (ciffer >= '0' && ciffer <= '9')
      ciffer_number = ciffer - '0';
    else if (ciffer >= 'a' && ciffer <= 'z')
      ciffer_number = ciffer - 'a' + 10;
    else ciffer_number = -1;   /* error */

    if (ciffer_number >= 0 && ciffer_number < base)
      res = res * base + ciffer_number;

    ciffer_ptr++; ciffer = *ciffer_ptr;
  }
  while (ciffer != '\0');

  return res;
}