triangle.cpp

这我们老师对是面向对象程序设计（清华大学出版社）一书制作的PPT

#include<iostream.h>
#include<math.h>
class Triangle;
class Cpoint
{
	float x,y;
public:
	Cpoint(float x1,float y1)
	{x=x1;y=y1;}
	void disp()
	{
		cout<<x<<"  "<<y<<endl;
	}
	//friend class Triangle;
	//friend float Triangle::distance(Cpoint&t1,Cpoint&t2);
	//friend float Triangle::area();
	friend float distance(Cpoint&,Cpoint&);

};
class Triangle
{
	Cpoint a,b,c;
public:
	Triangle(float x1,float y1,float x2,float y2,float x3,float y3):a(x1,y1),b(x2,y2),c(x3,y3)
	{
	}
    
	friend float area(Triangle&);
	friend float distance(Cpoint&,Cpoint&);
	friend float circumference(Triangle&);
};
float distance(Cpoint &t1,Cpoint &t2)
	{
		return  sqrt((t1.x-t2.x)*(t1.x-t2.x)+(t1.y-t2.y)*(t1.y-t2.y));
	}
float area(Triangle &x)
{	
		float l1,l2,l3,s;
		l1=distance(x.a,x.b);
		l2=distance(x.a,x.c);
		l3=distance(x.b,x.c);
		s=(l1+l2+l3)/2;
		return sqrt(s*(s-l1)*(s-l2)*(s-l3));
}
float circumference(Triangle&x)
{
	float l1,l2,l3;
	l1=distance(x.a,x.b);
	l2=distance(x.a,x.c);
	l3=distance(x.b,x.c);
	return l1+l2+l3;
}
void main()
{
	Triangle ta(0,0,2,0,0,2);
	cout<<area(ta)<<endl;
	cout<<circumference(ta)<<endl;
}