//pointer1.cpp
#include<iostream>  
//cout, cin, endl
using namespace std;

int main()
{
  int TomsAge=35;
  int SuesAge=43;

  int * pAge=0;
    //a pointer to an integer.
    //Initialize it!
    //It is pointing to location 0, not the number 0.

  cout << "The address IN pAge: "
       << pAge << '\n';
  cout << "The address OF pAge: "
       << &pAge << '\n';

  pAge=&TomsAge;  //store the address.
                  //say, pAge POINTS TO TomsAge
  if (pAge!=0) //don't dereference null pointer! 
    cout << "Tom's age: " << *pAge << '\n';
         //*pAge, dereferencing a pointer,
         //the VALUE that pAge is pointing to
  cout << "The address IN pAge: " << pAge << '\n';
  cout << "  is the address OF TomsAge " 
    << &TomsAge << '\n';
  cout << "The address OF pAge: "
       << &pAge << " does not change." << '\n';

  if (pAge!=0)
    {
    *pAge=36; //change the value in the box.
              //*pAge can be an l-value
    cout << "Tom's age: " << *pAge << '\n';
    }
  cout << "The address IN pAge: " << pAge << '\n';

  if (pAge!=0)
    {
    *pAge= SuesAge;
     //are we moving the pointer or changing 
     //the data?   In which box?
    cout << "The age pointed to is " 
      << *pAge << '\n';
    }
  cout << "Is it Sue's age?: "<< SuesAge << '\n';
  cout << "Is it Tom's age?: " << TomsAge << '\n';
  cout << "The address IN pAge: " << pAge << '\n';

  //set things up again
  SuesAge=43;
  TomsAge=35;
  pAge=&TomsAge;
  
  cout << "Now to see pointers can move:\n";
  cout << "   pAge is pointing to TomsAge " << *pAge << endl;
  cout << "      The address IN pAge is the address of TomsAge  "
    << pAge << endl;
  pAge=&SuesAge;
  cout<<"   Now pAge is pointing to SuesAge "
    << *pAge << endl;
  cout << "      which is at the address " << pAge << endl;

  return 0;
}