简单的字符界面银行ATM系统，通过消息队列实现客户端和服务器通信，服务器运用多进程，客户端运用函数指针调用，有利于初学者学习-Simple character interface bank ATM system, the client and server communicate via message queues, using multi-process server, the client calls using function pointers, help beginners lear