OBOE: Need help understanding, possible type conversion issue
way too complicated:

int convertTo10(char *num_26, int len) {
  int tmp = 0;  //hold the output
  int i;  //indexing the input
  while (len--) tmp = tmp * 26 + (num_26[i++]-'A');
  return tmp;
}


note:
 1. "* 26" can be further simplified;


error checking could be built-in here, or somewhere else (better).
better structuring could get rid of one of the temporary variables.