函数fun的功能是将形参a所指结构体变量s中的数据进行修改，并把a中地址作为函数值返回主函数，在主函数中输出修改后的数据。-Function fun feature is the structure parameter a referred variable s in the data modification, and to a function value in the address as the return to the main function, in the main function of the modified output data.