Conversion from Binary to decimal - Need help

Question

Hi guys,
I am new here and learnt some very basic Java before. I have a program that is in C++(to convert a binary number to decimal) that I found in the internet that interest me a lot. I am thinking whether this can be re-write in Java. I have tried to searh for solution but to no avail. I am wondering whether you guys can suggest a solution to this. Below are the source code in C++ :
#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;
Appreciate your help. Thank you.
CK

Answer 1

So for Java, in your example, it takes a Java
String like "1001" and converts it to an int whose
value is one thousand and one. Can suggest a code for
this that takes user input str and convert to bin int.
I read books and noticed they are various ways to do
that. I am quite confused actually. It is like there
is no fix way to do that, unlike C++ which is more
easier to understand(in my opinion). Probably, because
I knew C better than Java.
The 'standard' way to take a String and convert it to an int...
int TempBin=Integer.parseInt(your_string);
You seem to be saying that you do not want to use the standard method, so you should not complain that there is no standard method. Here's some code that re-uses most of your modulo 10.
import java.io.*;
public class Test {
     public static void main(String []args) throws IOException {
          BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));
          String result=null;
          while(true) {
               String input=bf.readLine().trim();
               try {
                    long v=Long.parseLong(input);
                    result=toBin(v);
                    System.out.println(result);
               } catch(NumberFormatException e) {
                         System.out.println("Only enter 1 or 0, nothing else!");
               System.out.println();
       public static String toBin(long btemp) {
          long temp=btemp;
          do {
               if ((temp % 10)!=0 && (temp % 10)!=1) {
                    System.out.println("Invalid pattern! use 0's and 1's only\n\n");
                    return null;
               temp = (temp/10);
          } while (temp>0);
          // part 3 : Convertion
          int div = 1;
          int Dec = 0;
          long TempBin = btemp;
          do {
               Dec += (TempBin % 10)*div; // Note (2)
               div *= 2;
               TempBin = (TempBin/10);
          } while (TempBin>0);
          return ""+Dec;