把功能相对独立的程序段单独编写和调试，作为一个相对独立的模块供程序调用，就形成子程序 子程序可以实现源程序的模块化，可简化源程序结构，可以提高编程效率(A relatively independent program segment is written and debugged separately. As a relatively independent module for program calls, a subroutine is formed. Subroutine can mo