NO7——二分

int binsearch(int *t,int k,int n)
{//t为数组，k是要查找的数，n为长度，此为升序
    int low = 1,high = n,mid;
    while(low<=high)
    {
        mid = (low+high)/2;
        if(k == t[mid])
        return mid;
        else if(k<t[mid])
        high = mid-1;
        else
        low = mid+1;
    }
    return -1;
}