classes and structs
===================
A class is a logical method to organize data and functions in a same structure
They are declared using keyword class, whose functionality is similar to the one
of the C keyword struct, but with the posibility of including functions as 
members, moreover than only data.
ex:
class class_name
	{
	private:
	 member;

	public:
	 member;
	} object_name;

where class_name is the name for the class(user defined type) and the optional 
field object name is 1, or several valid object indetifiers, the body of declaration
can contain members that can be either data or function declarations and optional 
permission lables that can be any of these 3 keywords  
1. private 
2. public 
3. protective

private members: of a class are accessable only from other members of its same class
or from its friend class

protective members: are accessable in addition from members of the same class and
friend classes

public members: are accessable from anywhere where the class is visable
-----------------------------------------------
#include<iostream.h>
class crectangle
{
	int x, y; //data member
public:
	void set_values (int, int); //member function
	int area (void)
	{
		return (x*y);
	}
};
void crectangle::set_values(int a, int b) /*::scope operator, specify the 
						class to which  the member being 
						declared belongs to. this  is also 
						an assignment.*/
{
	x=a;
	y=b;
}
int main()
{
	crectangle rect;// declares rect as an object
	rect.set_values(3,4);// assigns values to rect
	cout <<"Area :"<< rect.area() << endl;// outputs result
	return 0;
}