Example: Quick Sort in Ascending Order in C

// Quick Sort in Ascending Order
#include <stdio.h>

// Function to swap two elements
void swap(int* a, int* b) {
    int t = *a;
    *a = *b;
    *b = t;
}

/* This function takes last element as pivot, places
   the pivot element at its correct position in sorted
   array, and places all smaller (smaller than pivot)
   to left of pivot and all greater elements to right
   of pivot */
int partition(int arr[], int low, int high) {
    int pivot = arr[high]; // pivot
    int i = (low - 1);     // Index of smaller element

    for (int j = low; j <= high - 1; j++) {
        // If current element is smaller than the pivot
        if (arr[j] < pivot) {
            i++; // increment index of smaller element
            swap(&arr[i], &arr[j]);
        }
    }
    swap(&arr[i + 1], &arr[high]);
    return (i + 1);
}

/* The main function that implements QuickSort
   arr[] --> Array to be sorted,
   low   --> Starting index,
   high  --> Ending index */
void quickSort(int arr[], int low, int high) {
    if (low < high) {
        // pi is partitioning index, arr[pi] is now at right place
        int pi = partition(arr, low, high);

        // Separately sort elements before partition and after partition
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}

// Function to print an array
void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++)
        printf("%d ", arr[i]);
    printf("\n");
}

int main() {
    // Step 1: Define the array to be sorted
    int arr[] = {10, 7, 8, 9, 1, 5};
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Original array: ");
    printArray(arr, n);

    // Step 2: Call quickSort function to sort the array
    quickSort(arr, 0, n - 1);

    // Step 3: Print the sorted array
    printf("Sorted array in ascending order: ");
    printArray(arr, n);

    return 0;
}