c语言：用二分查找算法，查找有序数组的下标

#include<stdio.h>
int main()
{
  int arr[] = { 1,2,3,4,5,6,7,8,9 };
  int k = 7;

  int sz = sizeof(arr) / sizeof(arr[0]);
  int left = 0;
  int right = sz - 1;

  while (left<=k)
  {
    int mid = left + right / 2;
    if (arr[mid] > k)
    {
      right = mid - 1;
    }
    else if (arr[mid] < k)
    {
      left = mid - 1;
    }
    else
    {
      printf("下标是：%d\n", mid);
      break;
    }
  }
  if (left > right)
  {
    printf("找不到\n");
  }
  return 0;
}