/* This program demonstrates how to declare, initialize and dereference pointers
 * A pointer is a variable that stores the address of another variable.
 */

#include<iostream>
using namespace std;
int main()
{
	int *ptr; //This is a pointer of integer type. The * operator is used to declare a pointer.

	int x = 5; //Regular integer varibale.

	ptr = &x; // The & operator indicates the address of x.
	// ptr now stores the address of x.
	
	//We can have multiple levels of pointers.
	int **q; //this is a 2 level pointer. This can store the address of a pointer

	q = &ptr; //q no stores the address of ptr

	//dereferencing the process of acessing the value stored in the address pointed to by a pointer.
	//The * operator, when used with a pointer in any place other than declaration, dereferences the pointer

	cout<<"X is "<<x<<endl; //prints 5
	cout<<"Address of x is "<<&x<<endl; //prints an address
	cout<<"ptr is "<<ptr<<endl; //prints same as previous line
	cout<<"*ptr is "<<*ptr<<endl; //prints 5
	cout<<"Address of ptr is "<<&ptr<<endl; //prints address of ptr
	cout<<"q is "<<q<<endl; //prints the same as previous line
	cout<<"*q is "<<*q<<endl; //prints address of x
	cout<<"**q is "<<**q<<endl;//prints 5
	cout<<"Address of q is "<<&q<<endl; //prints address of q

	//Pointers usually store addresses of variables of the same type. 
	//If we want to force assignment of another type of pointer, we need to reinterpret cast
	double *dp = <reinterpret_cast>(double) ptr;
	
	//Dereferencing works for reading in values as well
	//If we read a dereferenced pointer, the original variable is also affected
	cin>>*ptr; // x now has a new value

	//The null pointer is a special pointer that points to nothing.
	//dereferencing a null pointer will result in a segfault
	//NULL, null and 0 mean the same thing when assigned to a pointer
	
	q = null; //q is now null
	
	return 0;
}