Homework: Define a virtual base class Shape, then derive five class: Circle, Square, Rectangle, Trapezoid and Triangle. Using virtual funciton to work out and display the area of every graph. And get the sum of these graphs. Tomorrow, oh no, it has, I will learn the last but one Chapter:I/0 stream. Also, hope it is not too difficult. #include <iostream> #include <cmath> using namespace std; const float Pi=3.14; class Shape { public: Shape(){} virtual float getAreaValue() const { return 0.0; } virtual void printArea() const = 0; }; class Circle : public Shape { public: Circle() { radius=0.0; } Circle(float r) { radius=r; } virtual void printArea() const; virtual float getAreaValue() const; private: float radius; }; void Circle::printArea() const { cout << "Circle Area:"; cout << P...