qsort.c

// Sorts an array of ints using Quicksort algorithm

#include <stdio.h>

#define N 10

void quicksort(int a[], int low, int high);
int split(int a[], int low, int high);

int main()
{
    int a[N], i;

    printf("Enter %d numbers to be sorted: ", N);
    for (i = 0; i < N; i++) scanf("%d", &a[i]);
    quicksort(a, 0, N - 1);
    printf("In sorted order: ");
    for (i = 0; i < N; i++) printf("%d ", a[i]);
    printf("\n");

    return 0;

}

void quicksort(int a[], int low, int high)
{
    int middle;

    if (low >= high) return;
    middle = split(a, low, high);
    quicksort(a, low, middle - 1);
    quicksort(a, middle + 1, high);
}

int split(int a[], int low, int high)
{
    int part_element = a[low];

    for(;;)
    {
        while (low < high && part_element <= a[high]) high--;
        if (low >= high) break;
        a[low++] = a[high];
        
        while (low < high && a[low] <= part_element) low++;
        if (low >= high) break;
        a[high--] = a[low];
    }

    a[high] = part_element;
    return high;
}