K&R Recursive Quicksort in C

quicksort.c

/* Pg. 87 - The C Programming Language (2nd Ed) - Recursive Quicksort */

/* qsort: sort v[left]..v[right into increasing order */
void qsort(int v[], int left, int right)
{
  int i, last;
  void swap(int v[], int i, int j);
  
  if (left >= right)                    /* do nothing if array contains */
    return;                             /* fewer than two elements */
  swap(v, left, (left + right) / 2);    /* move partition elem */
  last = left;                          /* to v[0] */
  for (i = left + 1; i <= right; i++)   /* partition */
    if (v[i] < v[left])
      swap(v, ++last, i);
  swap(v, left, last);                  /* restore partition elem */
  qsort(v, left, last - 1);
  qsort(v, last + 1, right);
}

/* swap: interchange v[i] and v[j] */
void swap(int v[], int i, int j)
{
 int temp;

 temp = v[i];
 v[i] = v[j];
 v[j] = temp;
}