Quick Sort in C

// C Program to sort an array using qsort() function in C
#include <stdio.h>
#include <stdlib.h>

// If a should be placed before b, compare function should
// return positive value, if it should be placed after b,
// it should return negative value. Returns 0 otherwise
int compare(const void* a, const void* b) {
    return (*(int*)a - *(int*)b);
}

int main() {
    int arr[] = { 4, 2, 5, 3, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
	
  	// Sorting arr using inbuilt quicksort method
    qsort(arr, n, sizeof(int), compare);

    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);

    return 0;
}

// C program to implement Quick Sort Algorithm
#include <stdio.h>

void swap(int* a, int* b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int partition(int arr[], int low, int high) {

    // Initialize pivot to be the first element
    int p = arr[low];
    int i = low;
    int j = high;

    while (i < j) {

        // Find the first element greater than
        // the pivot (from starting)
        while (arr[i] <= p && i <= high - 1) {
            i++;
        }

        // Find the first element smaller than
        // the pivot (from last)
        while (arr[j] > p && j >= low + 1) {
            j--;
        }
        if (i < j) {
            swap(&arr[i], &arr[j]);
        }
    }
    swap(&arr[low], &arr[j]);
    return j;
}

void quickSort(int arr[], int low, int high) {
    if (low < high) {

        // call partition function to find Partition Index
        int pi = partition(arr, low, high);

        // Recursively call quickSort() for left and right
        // half based on Partition Index
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}

int main() {
  
    int arr[] = { 4, 2, 5, 3, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);

    // calling quickSort() to sort the given array
    quickSort(arr, 0, n - 1);

    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);

    return 0;
}