二分查找

#include<stdio.h>
int fn(int * a,int n,int x)
{
    int s=0,e=n-1;
    int mid;
    while(s<=e)
    {
        mid=(s+e)>>1;
        if(a[mid] == x) return mid;
        else if(a[mid] > x) e=mid-1;
        else s=mid+1;
    }
    return -1;
}
int main()
{
    int i,a[10];
    for(i=0;i<10;i++)
    {
        a[i]=i*2;
    }
    while(1)
    {
        scanf("%d",&i);
        printf("%d\n",fn(a,10,i));
    }
    return 0;
}