#include<stdio.h>
#include<Windows.h>
int main()
{
 int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
 int mid = 0;
 int left = 0;
 int right = sizeof arr / sizeof arr[0] - 1;
 int key = 7;
 while (left<=right)
 {
  mid = left + (right - left) / 2;  //計算中間下標（防止溢位）
  if (arr[mid] < key)
  {
   left = mid + 1;
  }
  else if (arr[mid]>key)
  {
   right = mid - 1;
  }
  else
  {
   printf("找到了:%d\n", mid);
   break;  //找到了返回下標
  }
 }
 if (left > right)
  printf("-1\n");  //找不到返回-1
 system("pause");
 return 0;
}