Código para Qsort en C con intercambio

/* qsort: sort v[left]...v[right] into increasing order */
void qsort(int v[], int left, int right)
{
    int i, last;

    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;
}
Zealous Zebra