将上题以多文件方式组织，在area.h中声明各个area函数原型，在area.cpp中定义函数，然后在Exp9_2.cpp中包含area.h，定义main函数并执行-Many documents will be on the title to be organized in each area area.h declare the function prototype is defined in the area.cpp function, and then included in the Exp9_2.cpp area.h, the definition of main functions and implementation