quick sort algorithm

qsort.c

void qsort(int *a, int l, int r)
{
    int i, j, mid;
    i = l; j = r;
    mid = a[(i + j)/2];
    do {
        while (a[i] < mid) i++;
        while (a[j] > mid) j--;
        if (i <= j) {
            int temp = a[i];
            a[i] = a[j];
            a[j] = temp;
            i++; j--;
        }
    }while (i<=j);
    if (l < j) qsort(a, l, j);
    if (i < r) qsort(a, i, r);
}