Using member variables and member functions of a class

Use a ： Object name . Member name

#include <iostream>
using namespace std;
class crectangle
{
public:
	int w, h;//w and h Is a member variable 
	void Init(int w_, int h_)// This function is used to initialize , Set width and height , So this function is also a member function 
	{
		w = w_;
		h = h_;
	}
	int area()// Here are three member functions 
	{
		return w * h;
	}
	int perimeter()
	{
		return 2 * (w + h);
	}

};
int main()
{
	int w1, h1;
	cin >> w1 >> h1;
	crectangle r;//r It's an object 
	r.Init(w1, h1);// call Init Member functions 
//r.Init explain Init The function acts on r The above object , Enter Init In member function ,w1 and h1 All belong to r This object ,
// It also indicates that this member function will affect r Inside w1 and h1
	cout << r.area() << endl << r.perimeter();
	return 0;
}

Use two ： The pointer —> Member name

#include <iostream>
using namespace std;
class crectangle
{
public:
	int w, h;//w and h Is a member variable 
	void Init(int w_, int h_)// This function is used to initialize , Set width and height , So this function is also a member function 
	{
		w = w_;
		h = h_;
	}
	int area()// Here are three member functions 
	{
		return w * h;
	}
	int perimeter()
	{
		return 2 * (w + h);
	}

};
int main()
{
	int w, h;
	crectangle r1,r2;
	crectangle* p1 = &r1;
	crectangle* p2 = &r2;
	p1->w = 5;// to r1 Medium w The assignment is 5,h The assignment is 6
	p1->h = 6;
	p2->Init(6, 7);//Init It works on p2 Point to the object , namely r2
	cout << r1.area() << endl << r1.perimeter()<<endl;
	cout << r2.area() << endl << r2.perimeter();
	return 0;
}

Use three ： Reference name . Member name

int main()
{
	int w, h;
	crectangle r1;
	crectangle& rr = r1;//rr Refer to the r1, therefore rr and r1 It's actually the same thing 
	rr.w = 5;//rr The value of has changed ,r1 And the value of 
	rr.Init(5, 4);
	cout << r1.area() << endl << r1.perimeter() << endl;
}