二分法查找（数组元素无序）

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

int *bubble_sort(int a[],int n)//冒泡排序（将数据升序排列）
{
	int i;
	int j;
	int tmp;

	for(j=0;j<n-1;++j)//n个元素需要排序n-1趟
	{
		for(i=0;i<n-j-1;++i)//第j趟需要比较n-j次，第一趟（j=0）需要比较n-1次，n-j-1
		{
			if(a[i] > a[i+1])
			{
				tmp = a[i];
				a[i] = a[i+1];
				a[i+1] = tmp;
			}
		}
	}
	return a;
}
int binary_search(int b[],int n,int num)//二分法查找
{
	int left = 0;
	int right = n-1;
	int mid;
	
	while(left <= right) //若left <= right说明比较还未完成
	{
		mid = (left + right)/2;

		if(num < b[mid])//所寻找元素在mid的左边     
		{
			right = mid -1;
		}
		else if(num > b[mid])//所寻找元素在mid的右边
		{
			left = mid +1;
		}
		else 
		{
			return mid;
		}
	}
	return -1;//left > right时说明比较完成后，仍未找到该元素
}
int main()
{
	system("mode con cols=100 lines=100");
	system("color 0A");

	int b[] = {34,45,23,13,57,85,37,10};//数组元素未排序
	int n = sizeof(b)/sizeof(b[0]);
	int i;    //循环因子
	int num;  //要寻找的元素
	int ret;  //接收二分法查找函数的返回值

	bubble_sort(b,n); //二分法查找的前提，元素已经是有序的（将数组元素升序排列）
	for(i=0;i<n;i++)
	{
		printf("%d\n",b[i]);
	}

	printf("please input the num you want to find:\n");
	scanf("%d",&num);

	ret = binary_search(b,n,num);
	if(ret == -1)
	{
		printf("it is not exist!\n");
	}
	else
	{
		printf("it's subscript is %d\n",ret);
	}

	system("pause");
	return 0;
}