二分查找

int binary_search(int *a,int len,int goal)
{
    int low,high,mid;
    low=0;
    high=len-1;

    while(low<=high)
    {
        mid=(low+high)/2;
        if(goal==a[mid])
            return mid;
        else if(a[mid]<goal)
            low = mid+1;
        else
            high =mid-1;
    }
    return -1;
}