SORTING : QUICK SORT

#include < stdio.h >
void quicksort(int arr[],int left,int right);
int main()
{
    int a[25],n,i;
    printf("How many elements : ");
    scanf("%d",&n);
    for(i=0;i < n;i++)
    a[i]=rand()%100;
     for(i=0;i<n;i++)
    printf(" %d  \t",a[i]); 
    a[n]=500;              
    quicksort(a,0,n-1); 
    printf("\n sorted array is : \n");
    for(i=0;i<n;i++)
    printf(" %d  \t",a[i]); 
    getch();                
    return 0;
    }
void quicksort(int arr[],int left,int right)
{
int i,j,pivot,temp;
if(left<right)
{
              int i=left,j=right+1;
              pivot=arr[left];
              do {
              do i++; while(arr[i]<pivot);
              do j--; while(arr[j]>pivot);
              if(i<j)
              {
                 temp=arr[i];
                 arr[i]=arr[j];
                 arr[j]=temp;    
                     }
                 }while(i<j);
    temp=arr[left];
    arr[left]= arr[j];
    arr[j]=temp;
    quicksort(arr,left,j-1);
    quicksort(arr,j+1,right);                 
              }     
}

Quick sort function is invoked with Left and Right boundaries 0,n-1.Initially we set PIVOT element is a[Left] and the function go forward and array is divided into 2 parts and quicksort function is called for both of the parts.For each part a separate sorting is made and again these parts are divided into sub parts recursively.
Quick sort technique Time complexity :
Best case : O(n)
Average case : O(n log n)
Worst case : O(n x n)
To sort a[1:n] the function invocation is quicksort(a,0,n-1)and Quick sort assumes that a[n] has been set a value at least as large as remaining data to sorted in array.I have used a[n] is 500 because array value never be over by 100.