多项选择题
A.先弹后减 B.先减后弹 C.先压后加 D.都不对
A.-1 B.0 C.不变 D.可变
A.S->top=p; B.p->next=S->top;S->top=p; C.p->next=S->top;S->top=p->next; D.p=S->top;S->top=p;