写一个程序，定义抽象基类shape， 由它派生3个基类，Circle（圆），Rectangle（矩形），Trapezoid（梯形）。用虚函数分别计算几种图形的面积，并求他们的和。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-Write a program that defines an abstract base class shape, it is derived from the three basic classes, Circle (round), Rectangle (rectangle), Trapezoid (trapezoid). Virtual functions were calculated using several graphics area, and find their sum. Requirements: The base class array of pointers, each element it points to a derived class object