ARQ协议的模拟实现.编写两个计算机程序p1，p2。p1模拟发送方：首先从界面读取待发送字符（每接受一个字符的输入），保存到文件file1.txt中，并启动计时器；p2模拟接收方，它从file1.txt中查找是否有新字符到来，并提供模拟界面给用户选择：

-ARQ protocol simulation. Written two computer programs p1, p2. p1 simulate the sender: First, to be sent from the interface to read characters (each character to accept an input), saved to a file file1.txt, and starts the timer　p2 analog receiver, it looks from file1.txt if a new Character arrival and provide analog interface to the user to select: