说明：  教材上的、网上现行的PID实现的C语言代码几乎都是用浮点型的数据来做的，本代码使用了一个整型变量来实现了PID算法
(Teaching materials on-line PID existing C-language code to achieve almost all to do with the floating-point data type, and this code uses an integer variable to implement the PID algorithm)