constants in cpp

1// various versions of const are explained below
2#include <iostream>
3class Entity {
4private:
5	int m_X, m_Y;
6	mutable int var; // can be modified inside const menthods
7	int* m_x, *m_y;// * use to create pointer in one line
8public:
9	int GetX() const // cant modify class variables
10	{
11		//m_X = 4;//error private member can't be modified inside const method
12		var = 5; // was set mutable
13		return m_X;
14	}
15	int Get_X()// will modify class 
16	{
17		return m_X;
18	}
19	const int* const getX() const  // returning a pointer that cannot be modified & context of pointer cannot be modified
20	{
21		//m_x = 4;
22		return m_x;
23	}
24	void PrintEntity(const Entity& e) {
25		std::cout << e.GetX() << std::endl;
26	}
27};
28int main() {
29	Entity e;
30	const int MAX_AGE = 90;
31   // MAX_AGE =100; error const var is stored in read only section in memory and we can't write to that memory
32	//  int const* a = new int; is same as const int* a = new int ;////but you can't change the context of pointer but can reassign it to a pointer something else
33	int * const a = new int; //can change the context of pointer but can't reassign it to a pointer something else
34   *a = 2;
35    a = &MAX_AGE;// error can't change it to ptr something else
36   	std::cout << *a << std::endl;
37	a =(int*) &MAX_AGE;
38	std::cout << *a << std::endl;
39}

1#define identifier value
2

1#define LENGTH 10   
2#define WIDTH  5
3#define NEWLINE '\n'