说明：  对于简单的 C 语言程序，一般在把头文件和程序定义文件放在一起，只有一个.c 定义文件即可。而对于复杂的程序，则多采用头文件包含的形式并通过多个定义文件实现。
(For a simple C language program, usually defined in the head file and program files together, there is only one. C definition file. For the complicated programs, in the form of header file contains more and through multiple definition file. )