#include <stdio.h>  #include <stdlib.h>    #define SORT_ARRAY_SIZE       10000  #define PIVOT_FIRST           1  #define PIVOT_LAST            0  #define PIVOT_MEDIAN_OF_THREE 0    void QuickSort(int *array, int start, int end);  int ChoosePivot(int *array, int start, int end);    static long long compNum = 0;    int main() {      // load txt into array buffer      int *array = (int*)malloc(sizeof(int)*SORT_ARRAY_SIZE+10);      FILE *pFile;      pFile = fopen("QuickSort.txt", "r");      if (pFile == NULL)          perror("Error openin file.\n");      rewind(pFile);      for (int i = 0; i < SORT_ARRAY_SIZE; i++) {          fscanf(pFile, "%d", &array[i]);      }      fclose(pFile);        // quick sort array      QuickSort(array, 0, SORT_ARRAY_SIZE-1);      printf("number of comparisons is %lld\n", compNum);        free(array);      return 0;  }    void QuickSort(int *array, int start, int end) {      if (start >= end) return;      else if ((end - start == 1)&&(array[start]>array[end])) {          compNum += 1;          int temp = array[start];          array[start] = array[end];          array[end] = temp;      }      else {          compNum += (end - start);          // choose the pivot and do proper swap          int pivot = ChoosePivot(array, start, end);            // i denotes the location of pivot          int i = start + 1;          // j for loop the unpartitioned part          for (int j = start + 1; j < end + 1; j++) {              if (array[j] < pivot) {                  int temp = array[j];                  array[j] = array[i];                  array[i] = temp;                  i++;              }          }          // swap the pivot and array[i-1]          int temp = array[i-1];          array[i-1] = pivot;          array[start] = temp;            // quick sort the left and right partition          QuickSort(array, start, i-2);          QuickSort(array, i, end);      }  }    int ChoosePivot(int *array, int start, int end) {      int pivot = -1;  #if PIVOT_FIRST      // choose the first element as pivot      pivot = array[start];      return pivot;  #elif PIVOT_LAST      // choose the last element as pivot      // swap the first and the last element      pivot = array[end];      array[end] = array[start];      array[start] = pivot;      return pivot;  #elif PIVOT_MEDIAN_OF_THREE      // choose the median of first, mid and last      // element as pivot      int mid = (start + end) / 2;      int max = (array[start] > array[end]) ? (array[start]) : (array[end]);      max = (max > array[mid]) ? max : array[mid];       int min = (array[start] < array[end]) ? (array[start]) : (array[end]);      min = (min < array[mid]) ? min : array[mid];      if (array[start] != max && array[start] != min) {          pivot = array[start];          return pivot;      }      if (array[mid] != max && array[mid] != min) {          pivot = array[mid];          array[mid] = array[start];          array[start] = pivot;          return pivot;      }      if (array[end] != max && array[end] != min) {          pivot = array[end];          array[end] = array[start];          array[start] = pivot;          return pivot;      }  #endif  }