问题 单项选择题

一个采用顺序存储结构的栈,其中top为栈顶指针,若以地址高端作栈顶,地址低端作栈底,那么进行进栈操作时,对top的操作为( )。

A.top=top-1

B.top=top+1

C.top=0

D.top不做任何修改

答案

参考答案:B

解析: 栈是一种操作受限的线性表,只能在栈顶进行插入和删除操作,当进行入栈运算时,首先栈顶指针加1,指向一个空的存储空间,然后将数据写入该地址空间,因此选项B是正确的操作。选项A是进行出栈时的操作,选项C是置栈为空时的操作,选项D是读栈顶元素时栈顶指针保持不动的操作。

单项选择题
单项选择题

Electronic mail has become an extremely important and popular means of communication.

The convenience and efficiency of electronic mail are threatened by the extremely rapid growth in the volume of unsolicited commercial electronic mail. Unsolicited commercial electronic mail is currently estimated to account for over half of all electronic mall traffic, up from an estimated 7 percent in 2001, and the volume continues to rise. Most of these messages are fraudulent or deceptive in one or more respects.

The receipt of unsolicited commercial electronic mail may result in costs to recipients who cannot refuse to accept such mail and who incur costs for the storage of such mail, or for the time spent accessing, reviewing, and discarding such mail, or for both. The receipt of a large number of unwanted messages also decreases the convenience of electronic mall and creates a risk that wanted electronic mail messages, both commercial and noncommercial, will be lost, overlooked, or discarded amidst the larger volume of unwanted messages, thus reducing the reliability and usefulness of electronic mail to the recipient. Some commercial electronic mail contains material that many recipients may consider vulgar or pornographic in nature.

The growth in unsolicited commercial electronic mail imposes significant monetary costs on providers of Internet access services, businesses, and educational and nonprofit institutions that carry and receive such mail, as there is a finite volume of mail that such providers, businesses, and institutions can handle without further investment in infrastructure. Many senders of unsolicited commercial electronic mail purposefully disguise the source of such mall.

Many senders of unsolicited commercial electronic mall purposefully include misleading information in the messages’ subject lines in order to induce the recipients to view the messages. While some senders of commercial electronic mail messages provide simple and reliable ways for recipients to reject (or ’opt-out’ of) receipt of commercial electronic mall from such senders in the future, other senders provide no such ’opt-out’ mechanism, or refuse to honor the requests of recipients not to receive electronic mail from such senders in the future, or both.

Many senders of bulk unsolicited commercial electronic mail use computer programs to gather large numbers of electronic mail addresses on an automated basis from Internet websites or online services where users must post their addresses in order to make full use of the website or service.

The problems associated with the rapid growth and abuse of unsolicited commercial electronic mall cannot be solved by the government alone. The development and adoption of techno-logical approaches and the pursuit of cooperative efforts with other countries will be necessary as well.

"Pornographic" in Paragraph 3 probably means ().

A. decent

B. instructional

C. sexual

D. commercial