说明：  1. 编写一个基于流式套接字的C/S通信程序，客户端与服务器建立连接之后，客户端向服务器发送一个简单的四则算式（只含一个算符），服务器收到这个算式后，对其进行计算，并将计算结果回送给客户端，客户端将计算结果显示出来。要求： (1)服务器可以同时为多个客户提供服务。 (2)采用select模型实现。 2. 对于实验1的回射服务器采用select模型改写。 3.实现一聊天程序，要求采用WSAAyncSelect（异步选择）模型实现
(1. Write a C/S based on streaming socket communication program, the client and the server after the connection is established, the client to the server to send a simple four formula (containing only one operator), after the server receives this formula, the calculated, and the calculated results back to the client, the client to display results. Requirements: (1) the server can serve multiple clients at the same time. (2) using the model implementation. 2. As the experiment 1 echo server using the model. 3. Implement a chat program, require the use of WSAAyncSelect (asynchronous) model)