自建函數查找一個數組中一個指定數字的下标數

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int binary_search(int arr[], int k,int sz)
{
  //算法的實作
  int left = 0;
  int right = sz - 1;

  while (left <= right)
  {
    int mid = (left+right)/2;
    if (arr[mid] < k)//k為下表數
    {
      left = mid + 1;//小的話是在中間左面故left+1
    }
    else if (arr[mid] > k)
    {
      right = mid - 1;//大的話是在中間右面故right-1
    }
    else
    {
      return mid;
    }
    
  }
  return -1;
}
int main()
{
  int arr[] ={1,2,3,4,5,6,7,8,9,10};
  int k = 7;
  int sz = sizeof(arr)/sizeof(arr[0]);//求數組的元素個數
  int ret = binary_search(arr, k,sz);
  if (ret == -1)
  {
    printf("找不到指定的數字\n");
  }
  else
  {
    printf("找到了，下标是: %d\n", ret);
  }
}      

k = 7