模仿操作系统的先来先服务，用单链表写的程序-imitate the operating system first-come first-service, single-Chain written procedures

单链表的头文件，可以判断是否存在环，判断环的长度及入口点，还包括最基本的链表操作-Single list of header files, you can determine whether the length of the ring and the entry point to determine the existence of the ring, the list also includes the basic operation