声明抽象基类Shape，由它派生出3个子类：Circle（圆形）、Rectangle（矩形）、Triangle（三角形），用一个函数printArea分别求出以上三者的面积，三个图形的数据在定义对象时给定。再设计一个函数sumArea，求出三个图形面积之和。要求用基类指针数组，使它的每一个元素指向一个派生类对象。-Declares an abstract base class Shape, three sub-classes derived from it: Circle (round), Rectangle (Rectangle), Triangle (triangle), with a function printArea were calculated area of ​ ​ more than three, three graphics data in the definition given object. The redesign a function sumArea and obtained three graphics area. Requirements with a base class pointer array, each element points to make it a derived class object.