程序：运用函数找到所要求的数字下标

#include<stdio.h>
int binary_search(int arr[], int a, int len)
{
    int left = 0;
    int right = len - 1;
    int mid = 0;
    while (left <= right)
    {
         mid = (left + right) / 2;
        if (arr[mid]< a)
        {
            left = mid + 1;
        }
        else if (arr[mid] > a)
        {
            right = mid - 1;
        }
        else
        {
            return mid;
        }
    }
    return -1;
}
int main()
{   int a = 7;
    int arr[] = { 1,2,3,4,5,6,7,8,9,10 };
    int len= sizeof(arr) / sizeof(arr[0]);
    int ret = binary_search(arr, a,len);
    if (ret == -1)
    {
        printf("    \n找不到这个数字");
    }
    else
    {
        printf("    \n找到了下标为%d", ret);
    }
    return 0;
}