Question

Change low , high , and middle to be pointers to array elements rather than integers representing the array indices.
Change the split function to return a pointer, not an integer.

/* Sorts an array of integers using Quicksort algorithm */
/* Copyright K.N. King -- C programming Ch9.6 */

#include <stdio.h>

#define N 10

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

int main(void){

    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;
}

Answer 1

#include <stdio.h>

#define N 10

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

int main(void){

int a[N], i;

printf("Enter %d numbers to be sorted: ", N);
for(i = 0; i < N; i++)
scanf("%d", &a[i]);
int low=0,high=N-1;
quicksort(a, &low, &high);
  
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;
   int l=*low,r=*high;
middle = split(a, &l, &r);
int m1 = (*middle) - 1;
int m2 = (*middle) + 1;
l=*low;
r=*high;
quicksort(a, &l,&m1 );
quicksort(a, &m2, &r);
  
  
  
  
}

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;
}