写一个quick sort

#include <stdio.h>
#include <stdlib.h>

//int a[]={1000,10000,9,10,30,20,50,23,90,100,10};
int a[]={10,9,8,7,6,5};

int length=sizeof(a)/sizeof(int);

int swap(int start, int stop){
	int temp;
	temp=a[start];
	a[start]=a[stop];
	a[stop]=temp;
	return 0;
}

int  quicksort(int start, int stop) {

	int i;	

	int ostart=start;
	int ostop=stop;

	int k=a[start];
	int middle;
	if(start >= stop){
		return 0;
	}

	while( start <= stop ){

		printf("\n begin start=%d,stop=%d ,k=%d , ostart=%d,ostop=%d\n" , start, stop, k,ostart,ostop);
		int i;
		for(i=0;i<length;i++){
			printf("%d\n" , a[i]);
		}

		while((a[stop] >= k) &&(start<stop)){
			stop--;
		}

		while( (a[start] < k)  &&(start<stop)){
			start++;
		}

		if(start >= stop){
			break;
		}

		printf("after move start=%d,stop=%d ,k=%d , ostart=%d,ostop=%d\n" , start, stop, k,ostart,ostop);
	    if( start < stop ){
			swap(start,stop);
		}
		printf("may after swap start=%d,stop=%d ,k=%d , ostart=%d,ostop=%d\n" , start, stop, k,ostart,ostop);

	}
	quicksort(ostart, start);
	quicksort(stop+1, ostop);

}

int main(){

	printf("length= %d\n",length);
	int i;
	printf("\n");
	quicksort(0,length-1);
	printf("\n\n\n");
	for(i=0;i<length;i++){
		printf("%d\n" , a[i]);
	}
	printf("\n");

	return 0;
}

　　虽然这种算法烂大街，但是实现一个简洁、正确的算法还是不容易的。