Quick Sort

#include <stdio.h>
#include <stdlib.h>
void swap (int *x, int *y){
    if (x != y){
        *x += *y; *y = *x - *y; *x -= *y;
    }
 }
int partition(int a[], int start, int end){
    int pivotIndex = (start+end)/2; //can be anything between start and end.
    int pivotValue = a[pivotIndex], i = start - 1;
    swap(&a[pivotIndex], &a[end]);
    for(int j = start; j != end; j++)
        if(a[j] <= pivotValue) swap(&a[++i], &a[j]);
    swap(&a[i+1], &a[end]);
    return i+1;
}
void quickSort(int a[], int start, int end){
    if(start < end){
        int q = partition(a, start, end);
        quickSort(a, start, q - 1);
        quickSort(a, q + 1, end);
    }
}
int main(){
    int *a, i, n;
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    a = (int *) malloc(sizeof(int) * n);
    for(i = 0; i < n; i++) scanf("%d", &a[i]);
    quickSort(a, 0, n-1);
    for(i = 0; i < n; i++) printf("\t%d\t", a[i]);
}