/*
 **************************************************************************
 * Program name : 015_Binary_to_Decimal (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 : 2000/06/09 - first version                              *
 **************************************************************************
 * Description  : (a) input the a binary number                           *
 *                (b) convert to decimal number                           *
 *                (c) try again ?                                         *
 **************************************************************************
*/
#include <iostream.h>
#include <stdlib.h>

int main()
{
 // part 1 : declaration
 int  Bin, Dec, TempBin;
 int  div;
 char valid, again;

 do {
     // part 2 : Repeat asking the value of the binary number
     Bin = TempBin = 0;
     do {
         cout << "Please input a binary number (1 to 10 bits) : ";
         cin  >> Bin;
         TempBin = Bin;
         do {
             if ((TempBin % 10)==0 || (TempBin % 10)==1)             // Note (1)
               valid='Y';
             else {
                   cout << "Invalid pattern! use 0's and 1's only\n\n";
                   valid='N';
                   break;
                  };
             TempBin = (TempBin/10);
            } while (TempBin>0);
        } while (valid=='N');

     // part 3 : Convertion
     div = 1;
     Dec = 0;
     TempBin = Bin;
     do {
         Dec += (TempBin % 10)*div;                                  // Note (2)
         div *= 2;
         TempBin = (TempBin/10);
        } while (TempBin>0);
     cout << "\nThe binary pattern " << Bin << " is equal to "
          << Dec << " in decimal pattern.\n" << endl;

     // part 4 : try another number ?
     cout << "\aTry another number (Y/N) : ";
     cin  >> again;
     cout << "\n";
    } while (again=='Y' || again=='y');
 cout << "\n" << endl;

 system("PAUSE");
 return 0;
}

/* Notes
   (1) If the remainder of TempBin over 10 is not zero or one, then
       the program think that the binary pattern is invalid.

       Example :  Let's the value of TempBin is 1201 , then

       Round  TempBin  Remainder  Action
       ----------------------------------------------------------------
         1     1201        1      adjuct the value of TempBin to  120
         2     120         0      adjuct the value of TempBin to  12
         3     12          2      Error found! Stop the loop of checking
                                  invalid digit the this binary pattern.

   (2) Convertion :
       The line "Dec += (TempBin % 10)*div;" find the new value of Dec.
       The line "div *= 2;" adjust/update the value of div for the next round.
       The line "TempBin = (TempBin/10);" adjust/update the value of TempBin
       for the next round.

       Example :  Let's the value of TempBin is 1101 , then

       Round  Remainder  div  Old_Dec  New_Dec  New_div
       ----------------------------------------------------------------
         1       1        1      0     1*1+0=1     2
         2       0        2      1     0*2+1=1     4
         3       1        4      1     1*4+1=5     8
         4       1        8      5     1*8+5=13    16
*/