C++ 理解多态《C++多线程编程实战》

#include <iostream>

#define M_PI 3.14159265358979323846

using namespace std;

class CFigure
{
public:
	virtual const char* FigureType() = 0;
	virtual double Circumference() = 0;
	virtual double Area() = 0;
	virtual ~CFigure(){ }
};

class CTriangle : public CFigure
{
public:
	CTriangle()
	{
		a = 0;
		b = 0;
		c = 0;
	}
	CTriangle(double a, double b, double c) : a(a), b(b), c(c){ }
	virtual const char* FigureType()
	{
		return "Triangle";
	}
	virtual double Circumference()
	{
		return a + b + c;
	}
	virtual double Area()
	{
		double S = Circumference() / 2;
		return sqrt(S * (S - a) * (S - b) * (S - c));
	}

private:
	double a, b, c;
};

class CSquare : public CFigure
{
public:
	CSquare()
	{
		a = 0;
		b = 0;
	}
	CSquare(double a, double b) : a(a), b(b) { }
	virtual const char* FigureType()
	{
		return "Square";
	}
	virtual double Circumference()
	{
		return 2 * a + 2 * b;
	}
	virtual double Area()
	{
		return a * b;
	}

private:
	double a, b;
};

class CCircle : public CFigure
{
public:
	CCircle()
	{
		r = 0;
	}
	CCircle(double r) : r(r) { }
	virtual const char* FigureType()
	{
		return "Circle";
	}
	virtual double Circumference()
	{
		return 2 * r * M_PI;
	}
	virtual double Area()
	{
		return r * r * M_PI;
	}

private:
	double r;
};

int main()
{
	CFigure* figures[3];

	figures[0] = new CTriangle(2.1, 3.2, 4.3);
	figures[1] = new CSquare(5.4, 6.5);
	figures[2] = new CCircle(8.8);
	for (int i = 0; i < 3; i++)
	{
		cout << "Figure type:\t" << figures[i]->FigureType()
			 << "\nCircumference:\t" << figures[i]->Circumference()
			 << "\nArea:\t" << figures[i]->Area()
		     << endl << endl;
	}

    return 0; 

运行结果