main-pointers.cpp

#include <iostream>
 
using namespace std;
 
int main ()
{
//The computer assigns to A the address of the memory cell 0x00
//and stores in its data area the value 5
int A = 5;
//With the operator & I get the address of A then the instruction
//print the address 0x00 on the screen
cout << &A << endl;
//I declare a variable B, pointer of type int, to which the computer 
//assigns the memory cell to the address 0x01, then this variable is used 
//to store the address of A.
int* B = &A; // the computer assigns the memoy cell to B at the address 0x01,
                   // in this cell, the address of A 0x00 is stored
//The following statement causes a compilation error!
//This commented line has been inserted to emphasize that B
//is a variable of type int* (int pointer) and as such can receive
//as a value only an address.
 
// B = 5; //Error ! B is of type int* (int pointer) is not of type int
 
//This instruction prints on the screen the data contained in the cell 
//whose address is stored in B. Since the address of A was previously 
//stored in B, the value 5 will be printed

cout << *B << endl; // print the cell data at the address
                     // contained in B i.e. 5
//B is a variable of type int* (int pointer) which can store an address,
//since it is a variable, however, the computer also assigns an address 
//to it. This instruction prints address of B on the screen

cout << &B << endl; // & gets the address of B assuming it is 0x01

//In this case, instead, the data contained in B is printed,
//but since B is a pointer that stores only addresses 
//and given that in it was previously stored the address
//of A, the data area contains is 0x00

cout << B << endl; // print the data contained in B,
                    // B is a pointer that stores the address of A i.e. 0x00
 
//The value to the cell pointed to by B is changed from 5 to 10,
//and since B points to the memory cell of A, it is the value of A that is changed.

 
*B = 10; // change the data of the cell pointed to by B, i.e. the value of the cell of A
 
cout << "Value value of A:" << A << endl;
cout << "Value contained in the cell pointed to by B:" << *B << endl;
 
return 0;
}