由点求面积

#include <iostream>
using namespace std;
class Rectangle
{
public:
	Rectangle(){x1=0;y1=0;x2=0;y2=0;}
	Rectangle(double X1,double Y1,double X2,double Y2):x1(X1),y1(Y1),x2(X2),y2(Y2){}
	Rectangle operator +(Rectangle &p)
	{
		 Rectangle P;
		 P.x1=x1+p.x1;
		 P.y1=y1+p.y1;
		 P.x2=x2+p.x2;
		 P.y2=y2+p.y2;
		 return P;

	}
	friend ostream& operator <<(ostream & output,Rectangle & p)
	{
		output<<(p.x2-p.x1)*(p.y2-p.y1)<<endl;
		return output;
	}

	void input()
	{
		cin>>x1>>y1>>x2>>y2;
	}
	void output()
	{
		cout<<(x2-x1)*(y2-y1)<<endl;
	}
private:
	double x1,y1,x2,y2;
};
int main()

{

    Rectangle p1(1,1,6,3),p2,p3;

    p2.input();

    p3=p1+p2;

    cout<<p3;

    return 0;

}