問題及程式碼：

#include <stdio.h>
int binary_search(int arr[], int n, int k);
#define SIZE 10
int main( )
{
    int d[SIZE] = {1,3,9,12,32,41,45,62,75,77};
    int key,index;
    printf("Input a key you want to search: ");
    scanf("%d", &key);
    index = binary_search(d, SIZE, key);
    if(index >= 0)
        printf("The index is %d .\n", index);
    else
        printf("Not found.\n");
    return 0;
}

int binary_search(int arr[],int n,int k)
{
    int i=-1;
    int low=0,high=n-1,mid;
    while(low<=high)
    {
        mid=(low+high)/2;
        if(arr[mid]==k)
        {
            i=mid;
            break;
        }
        else if(arr[mid]>k)
        {
            high=mid-1;
        }
        else
        {
            low=mid+1;
        }
    }
    return i;
}