Area Problem

[williambj15]

2.1 - Design a class point that has x and y coordinates as data members:
Include the following member functions:
 Constructor with arguments
 Constructor without arguments (Default constructor)
 Scale function: void scale(double a)
This function is supposed to scale the coordinates of the point by a, i.e., multiply each by the
real number a.
 Add function: void add(point q)
If p and q are of type point, the function p.add (q) should modify p in such a way that:
p.x is assigned p.x + q.x, and p.y is assigned p.y + q.y.
2.2 Based on the class point, design a class rectangle that defines a rectangle as follows:
In this problem, by a rectangle we mean a rectangle whose edges are either vertical or horizontal
(i.e., we do not deal with rotated rectangles). Thus to specify a rectangle we only need to specify
its lower left corner point and its upper right corner point.
Include the member functions:
 Constructor with arguments which allows the user to initialize a rectangle by specifying its 2 defining corner points.
 Constructor without arguments (Default constructor)
 Area member function : double area()
 Scale member function: void scale(double a)
This function is supposed to scale each of the corner points of the rectangle by a.
 Translate member function: void translate(point q)
This function is supposed to translate the rectangle by the vector q, i.e., add q to both corner points.
 containsPoint member function: bool containsPoint(point p)
This function is supposed to check if a given point p is inside the rectangle.
 The pointSetIntersect function:
void pointSetIntersect(point A[], int n, point B[], int &m)
This function is supposed to store in the array B all the points in A[0 . . . n − 1] which are
inside the rectangle. It is supposed also to set m to the number of points in A[0 . . . n − 1]
which are inside the rectangle.
Write a program to test your classes and functions

#include <iostream>
#include <cmath>
using namespace std;

class point
{ 
	friend class rectangle;
	private:
		double x,y;

	public:
		point()
		{x=y=0;}

		point(double a, double b)
		{
			x=a;
			y=b;
		}

		void scale(double a)
		{
			x=x*a;
			y=y*a;
		}
	
		void add(point q)
		{
			x= x+ q.x;
			y= y+ q.y;
		}

		double getx()
		{
			return x;
		}

		double gety()
		{
			return y;
		}
};

class rectangle
{
private:
	
	point p1,p2;
public:

	rectangle (point c1, point c2)
	{
		p1=c1;
		p2=c2;

	}

	rectangle ()
	{
		point p;
		p1=p;
		p2=p;
	}

	double area()
	{
		double H=fabs(p1.y-p2.y);
		double W=fabs(p1.x-p2.x);
		return (H*W);
	}

	void scale (double a)
	{
		p1.scale(a);
		p2.scale(a);
	}

	void translate (point q)
	{
		p1.add(q);
		p2.add(q);
	}

	bool containsPoint(point p)
	{
		if( (p.x > p1.x && p.x < p2.x) && (p.y < p1.y && p.y > p2.y))
			return true;
		else
			return false;
	}

	void pointSetIntersect (point * A, int n, point * B)
	{
	    int K=0;
		int m=0;
		for(int i=0; i<n; i++)
		{
			if(containsPoint (A[i]))
			{ B[K]=A[i];
			K++;
			m++;
			}
		}
	}
}; //end of class rectangle.

void main()
{
	point p(5,6);


	p.scale(5);
	cout<<"P is now: "<< p.getx()<<" "<< p.gety()<<endl;

	p.add(p);
	cout<<"P is now: "<< p.getx()<<" "<< p.gety()<<endl;

    rectangle r;
	cout<<"Area is: "<<r.area ()<<endl;
	r.scale(6);
	r.translate(p);
	r.containsPoint (p);
	point A,B;
	r.pointSetIntersect(&A,7,&B);
}

Why the area always is giving me 0 can somebody correct my error

[ne555]

> Why the area always is giving me 0

rectangle r;
cout<<"Area is: "<<r.area ()<<endl;

¿what are the vertices of the `r' rectangle?
¿what should be its area then?

[williambj15]

so i didn't understand what should i do ??