classes

[butterflyze]

we are learning about classes in my c++ class and we are currently assigned to work on a class that will basically output the area of two rectangles. We are required to set the initial height and width both to 0.0. Also, we must set height = h and width = w. I think the code will speak for itself:

Header:
#ifndef RECTANGLE_H
#define RECTANGLE_H

class rectangle
{
	float height;
	float width;
	float area;

public:
	//bool operator==(const rectangle&);
	friend istream &operator>>(istream &, rectangle&);
	friend ostream &operator<<(ostream &, const rectangle&);
	rectangle();
	rectangle(float h, float w);
   // rectangle (rectangle &r);
	float getarea(float, float);
	float getrectangle();
	

};
#endif





Function Implementation:
#include <iostream>
using namespace std;

#include "rectangle.h"

rectangle::rectangle()
{
	height = 0.00;
	width = 0.00;
	
}

rectangle::rectangle(float h, float w)
{
	height = h;
	width = w;
}

//rectangle::rectangle(rectangle &r)
//{
//	height = r.height;
//	width = r.width;
	
//}

float rectangle::getarea(float h, float w)
{
	area = width * height;
	return area;
}





//bool rectangle::operator==(const rectangle &r)
//{
	//if ()
		
	//	return false;
	//else 
		
	//	return true;
	
//}

istream &operator>>(istream &is, rectangle&r)
{
	cout << "Enter the height and width." << endl;
	is >> r.height >> r.width;
	return is;
	

}

ostream &operator<<(ostream &os, const rectangle&r)
{
	os << "The area is: " << r.area << endl;
	return os;

}





Test Program:
#include <iostream>
using namespace std;

#include "rectangle.h"

int main()
{
	
	rectangle r1, r2(5.0, 5.0);
	cin >> r1;
	cout << r1;
	cout << r2;
	

	//if(r1 == r2)
		//cout << "The rectangles are equal." << endl;
	//else
		//cout << "The rectangles are not equal." << endl;
	
	return 0;
}

Ignore the commented code....That is something I am working on adding on to it. The end result is that we are supposed to compare two rectangles through an overloaded "==" function and output if they are equal or not. However, before I add the extras, there seems to be a problem with initialization somewhere involving the height and width. The program compiles but the area comes out to a strange exponential number. thanx.

[bluecoder]

why passing parameters to

float rectangle::getarea(float h, float w)
{
	area = width * height;
	return area;
}

you have not assigned the value to area variable .

ostream &operator<<(ostream &os, const rectangle&r)
{
	os << "The area is: " << r.area << endl;
	return os;

}

directly printing the value of area which will be 0 or uninitialized .

[butterflyze]

why isnt area initialized when i do the calculation "area = width * height"? Im not sure I understand.

[idbentley]

You don't do the calculation area = width * height in your constructor, so when you build the object, area is still unset.

You can change this by changing:

rectangle::rectangle(float h, float w)
{
	height = h;
	width = w;
}

//rectangle::rectangle(rectangle &r)
//{
//	height = r.height;
//	width = r.width;
	
//}

float rectangle::getarea(float h, float w)
{
	area = width * height;
	return area;
}

to

rectangle::rectangle(float h, float w)
{
	height = h;
	width = w;
	area = width * height;
}

It is also worth changing the default constructor to include a default area.

rectangle::rectangle()
{
	height = 0.00;
	width = 0.00;
        area = 0.00;
}

now in your main, whichever constructor was called, area will be defined. Before area was only defined when getarea was called (and you never called it).

Does that help?

[butterflyze]

yes i understand now thank you. now the only problem is that i enter two numbers....for the first object in the main.....and the area outputs zero all the time. the second object (r2(5.00, 5.00)) calculates perfectly but r1 outputs zero. I am guessing that it is because of setting area to zero in the constructor?

#include <iostream>
using namespace std;

#include "rectangle.h"


rectangle::rectangle()
{
	height = 0.00;
	width = 0.00;
	area = 0.00;
	
}

rectangle::rectangle(float h, float w)
{
	height = h;
	width = w;
	area = height * width;	
}

rectangle::rectangle(rectangle &r)
{
	height = r.height;
	width = r.width;
	area = r.height * r.width;
}

float rectangle::getarea()
{
	area = height * width;
	return area;
}

//float rectangle::getrectangle()
//{
	
//}

//bool rectangle::operator==(const rectangle &r)
//{
	//if ()
		
	//	return false;
	//else 
		
	//	return true;
	
//}

istream &operator>>(istream &is, rectangle&r)
{
	cout << "Enter the height and width." << endl;
	is >> r.height >> r.width;
	return is;
	

}

ostream &operator<<(ostream &os, const rectangle&r)
{
	os << "\nThe height is: " << r.height << "\nThe width is: " << r.width << endl;
	os << "\nThe area is: " << r.area << endl;
	return os;

}

of course if i cin the area in the main, then it will display the value that i put in. But that defeats the purpose really.

[imi]

actually I would recommend you remove area completely as member variable and always calculate it "on the fly" in getarea.

Then you don't print out r.area in your cout<< statement, but call to r.getarea(). Sounds better to me.

...
class rectangle
{
	float height;
	float width;
	//float area;  <-- don't store it as class variable
...
	float getarea() const { return height*width; }
};
...
    os << "The area is: " << r.getarea() << endl;

Ciao, Imi.

[mcleano]

I agree with imi. More importantly though make sure you do remove area from the constructor. The constructor is not there to perform calculations, it is there to initialize your object.

[butterflyze]

thank you imi and mcleano....it works perfectly now. thanks to everyone.