下面程序段的功能是实现二分查找算法，请在下划线处填上正确的语句。
struct record{int key; int others;};
int bisearch(struct record r[ ], int k)
{
int low=1,mid,high=n;
while(low<=high)
{
___1 ___;
if(r[mid].key==k)
return(mid);
else if(
r[mid].key>k
)
high=mid-1;
else
low=mid+1;
}
return(0);
}
