Nested Function

quick_sort.c

void sort(int *a, unsigned size) {
  
  void quick_sort(unsigned first, unsigned last) {

    void swap(unsigned i, unsigned j) {
      int tmp = a[i]; a[i] = a[j]; a[j] = tmp;
    }

    int partition() {
      int pivot = a[first];
      unsigned index = first;
      swap(index, last);
      
      for (unsigned i = first; i < last; i++) if (a[i] < pivot) swap(index++, i);
      swap(index, last);
      return index;
    }

    if (first < last) {
      unsigned pivotIndex = partition();
      quick_sort(first, pivotIndex - 1);
      quick_sort(pivotIndex + 1, last);
    }
  }

  quick_sort(0, size - 1);
}