/*
 **************************************************************************
 * Program name : 054_Const_qualifier_with_pointer (Version 1.00)         *
 * Author       : Duck Wong                                               *
 * Language     : C / C++                                                 *
 * Compiler     : Boodshed Dec-C++ compiler Ver 3.95                      *
 * Computer     : PII350                                                  *
 * O/S          : Windows 98                                              *
 **************************************************************************
 * Version 1.00 : 2000/07/01 - first version                              *
 **************************************************************************
 * Description  : (a) Input 4 integer number , output pointers' values    *
 *                (b) Re-input 4 integer number , output pointers' values *
 *                (c) Change the values of variable C & D and             *
 *                    output pointers values                              *
 *                (d) Change the values of pointers 2 & 4 and             *
 *                    output pointers values                              *
 *                (e) Try again ?                                         *
 **************************************************************************
*/
#include <iostream.h>
#include <stdlib.h>


int main()
{
 // part 1 : declaration
 char  Again;
 int A, B, C, D;

 do {
     // part 2a : Input four numbers
     cout << "\n\tPlease input an integer number (A): ";
     cin  >> A;
     cout << "\n\tPlease input an integer number (B): ";
     cin  >> B;
     cout << "\n\tPlease input an integer number (C): ";
     cin  >> C;
     cout << "\n\tPlease input an integer number (D): ";
     cin  >> D;
     // part 2b : Assign these numbers to pointers
     const int * const pointer_1 = &A;                               // Note (1)
     const int *       pointer_2 = &B;
           int * const pointer_3 = &C;
           int *       pointer_4 = &D;
     // part 2c : Output current status
     cout << "\n\n\tCurrent status : ";
     cout << "\n\tpointer_1 (A)" << "\t" << *pointer_1 << "\t" << pointer_1;
     cout << "\n\tpointer_2 (B)" << "\t" << *pointer_2 << "\t" << pointer_2;
     cout << "\n\tpointer_3 (C)" << "\t" << *pointer_3 << "\t" << pointer_3;
     cout << "\n\tpointer_4 (D)" << "\t" << *pointer_4 << "\t" << pointer_4;
     cout << "\n\t";
     system("PAUSE");

     // part 3a : Re-input four numbers
     cout << "\n\tPlease input an integer number (A): ";
     cin  >> A;
     cout << "\n\tPlease input an integer number (B): ";
     cin  >> B;
     cout << "\n\tPlease input an integer number (C): ";
     cin  >> C;
     cout << "\n\tPlease input an integer number (D): ";
     cin  >> D;
     // part 3b : Output current status
     cout << "\n\n\tAfter re-input the values of A,B,C and D : ";
     cout << "\n\tpointer_1 (A)" << "\t" << *pointer_1 << "\t" << pointer_1;
     cout << "\n\tpointer_2 (B)" << "\t" << *pointer_2 << "\t" << pointer_2;
     cout << "\n\tpointer_3 (C)" << "\t" << *pointer_3 << "\t" << pointer_3;
     cout << "\n\tpointer_4 (D)" << "\t" << *pointer_4 << "\t" << pointer_4;
     cout << "\n\t";
     system("PAUSE");

     // part 4a : Change the values of variable C & D w/ pointer
     // *pointer_1 = 1;              // error : assignment of read-only location
     // *pointer_2 = 2;              // error : assignment of read-only location
     *pointer_3 = 3;
     *pointer_4 = 4;
     // part 4b : Output current status
     cout << "\n\n\tAfter changing the values of variable C & D w/ pointer : ";
     cout << "\n\tpointer_1 (A)" << "\t" << *pointer_1 << "\t" << pointer_1;
     cout << "\n\tpointer_2 (B)" << "\t" << *pointer_2 << "\t" << pointer_2;
     cout << "\n\tpointer_3 (C)" << "\t" << *pointer_3 << "\t" << pointer_3;
     cout << "\n\tpointer_4 (D)" << "\t" << *pointer_4 << "\t" << pointer_4;
     cout << "\n\t";
     system("PAUSE");

     // part 5a : Change the values of pointer_2 & pointer_4
     // pointer_1 = &C;              // error : assignment of read-only variable
     // pointer_3 = &A;              // error : assignment of read-only variable
     pointer_2 = &A;
     pointer_4 = &C;
     // part 5b : Output current status
     cout << "\n\n\tAfter changing the values of pointers 2 and 4 : ";
     cout << "\n\tpointer_1 (A)" << "\t" << *pointer_1 << "\t" << pointer_1;
     cout << "\n\tpointer_2 (A)" << "\t" << *pointer_2 << "\t" << pointer_2;
     cout << "\n\tpointer_3 (C)" << "\t" << *pointer_3 << "\t" << pointer_3;
     cout << "\n\tpointer_4 (C)" << "\t" << *pointer_4 << "\t" << pointer_4;
     cout << "\n\t";

     // part 6 : try another number ?
     cout << "\n\n\tTry another number (Y/N) : ";
     cin  >> Again;
     cout << "\n";
    } while (Again=='Y' || Again=='y');
 cout << "\n" << endl;

 system("PAUSE");
 return 0;
}

/* Notes
   The use of CONST qualifier :

     syntex / format                       | *pointername | pointername
     --------------------------------------|--------------|----------------
     const int * const pointername = ....; | unmodifiable | unmodifiable
     const int *       pointername;        | unmodifiable |     ---
           int * const pointername = ....; |     ---      | unmodifiable
           int *       pointername;        |     ---      |     ---
     --------------------------------------|--------------|----------------
*/