C++ Programming - Practical 8

Exercise 1

Consider the base class shape,

shape.h

#ifndef shape_h
#define shape_h

#include <string>

class shape
{
public:
	virtual double area() = 0;
	virtual double perimeter() = 0;
	void describe();
	virtual std::string name();
protected:
	std::string color;
};

#endif

shape.cpp

#include "shape.h"
#include <iostream>

using namespace std;

void shape::describe()
{
	cout << "The " << color << " "
		 << name() << " has an area of "
		 << area() << " and a perimeter of "
		 << perimeter() << endl;
}

string shape::name()
{
	return("shape");
}

Note that here the virtual functions area() and perimeter() are declared =0 to indicate they have no implementation in the base class. A derived class for a rectangle might be as follows,

rectangle.h

#ifndef rectangle_h
#define rectangle_h

#include "shape.h"

class rectangle : public shape
{
public:
	rectangle(std::string color, double width, double height);
	double area();
	double perimeter();
	std::string name();
private:
	double width;
	double height;
};

#endif

rectangle.cpp

#include "rectangle.h"
#include <iostream>

using namespace std;

rectangle::rectangle(string c, double w, double h)
{
	color=c;
	width=w;
	height=h;
}

double rectangle::area()
{
	return(width*height);
}

double rectangle::perimeter()
{
	return(2*width+2*height);
}

string rectangle::name()
{
	return("rectangle");
}

and finally the test program,

test.cpp

#include "rectangle.h"
#include <vector>

int main()
{
	std::vector<shape*> shapes;

	rectangle r1("green", 10, 4);
	rectangle r2("red", 5, 8);

	shapes.push_back(&r1);
	shapes.push_back(&r2);

	for(int i=0; i<shapes.size(); i++)
		shapes[i]->describe();

	return 0;
}

Exercise 2