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); }