Callbacks in C

callback.c

// Only INT, don't trying use arrays with char
void foreach(int *arr, int len, void (*callback) (int item, int idx)) {
  unsigned idx = 0;
  for (idx; idx < len; idx++) 
    callback(arr[idx], idx);
}
int main() {
  int arr[] = {1, 3, 5, 6};
  int arr_len = sizeof arr / sizeof arr[0];
  void cb (int n, int idx) {
    printf("cb: %-3i:%2i\n", n, idx);
  }
  foreach(arr, arr_len, cb);
  return 0;
}