在整型有序数组中查找想要的数字， 找到了返回下标，找不到返回-1.（折半查找）

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
int BinarySearch(int a[], int key, int len)
{
	int ret = -1;//找到了返回下标，找不到返回-1.
	int left = 0;
	int right = len - 1;
	while (left <= right)
	{
		int mid = (left + right) / 2;
		if (a[mid] > key)
		{
			right = mid - 1;
		}
		else if (a[mid] < key)
		{
			left = mid + 1;
		}
		else
		{
			ret = mid;
			break;
		}
	}
	return ret;
}
int main()
{
	int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
	int size = sizeof(a) / sizeof(a[0]);
	int key;
	scanf("%d", &key);
	int ret = BinarySearch(a, key, size);
	if (ret != -1)
	{
		printf("找到了，下标为%d\n", ret);
	}
	else
	{
		printf("没找到\n");
	}
	system("pause");
	return 0;
}