Convert Binary Integer to Decimal

[Kinsleyy]

Hi I am trying to write an app that inputs an integer containing only 0s and 1s (a binary integer) and prints its decimal equivalent. I am aware that there are some very short ways to do this but as a beginner I am writing this to show the process. I am trying to use the remainder and division operators to complete this. Here is what I have, is there a different route I can take? Any help will be greatly appreciated! thanks

import java.util.Scanner;

public class BinarytoDecimal {

    
        
        
        public static void main(String[] args) {
       
                int r;
                int s = 0;
                int p = 1;
                

             Scanner in = new Scanner(System.in);
             System.out.println("Binary to Decimal");
             System.out.println("Enter a Binary Number which is to be converted");//ask to input the number which is to be converted
             int n= in.nextInt();
             

             

             


             while(n > 0)
             {
                 r = n % 10;
                 n = n / 10;
                 if(r!= 0 && r!= 1)
                 {
                     System.out.println("This is not a binary number.!!!");
                     System.out.println("Please try once again.!!!");
                     System.exit(0);//exits if the number is non binary
                 }
             }
            
             System.out.print("Binary="+n);
             {
             int temp = n;
             
             while(n>0)
             {
                 r=n%10;
                 s=s+(r*p);
                 p=p*2;
                 n=n/10;
             }
             System.out.print("converted to Decimal Number="+s);//generates output
 
             {}// Need ending brackets!
         } // End of main()
        }} // End of class

[Kinsleyy]

Any suggestions would help..PS I know there is an api to do this simple also. But I am trying to show the process

[WingedPanther]

You need to use multiplication and addition to go from binary to decimal, not modulus and division. You should probably accept the binary as a string.

[Kinsleyy]

Okay now I have this..What is wrong now. I need to find correct placement and format to inform the user to enter the binary integers..etc

public static long binaryToDecimal(String binary) throws NumberFormatException {
  // Initialize result to 0
  long res = 0;

  // Do not continue on an empty string
  if (binary.isEmpty()) {
    throw new NumberFormatException("Empty string is not a binary number");
  }

  // Consider each digit in the string
  for (int i = 0; i < binary.length(); i++) {
    // Get the nth char from the right (first = 0)
    char n = binary.charAt(binary.length() - (i+1));
   
    // Check if it's a valid bit
    if ((n != '0') && (n != '1')) {
      // And if not, die horribly
      throw new NumberFormatException("Not a binary number");
    } else if (n == '1') {
      // Only add the value if it's a 1
      res += Math.round(Math.pow(2.0, i));
    }
  }

  return res;
}

[WingedPanther]

res = res*2 + n.

[Kinsleyy]

Where does that need to be

[Kinsleyy]

Ok I figured it out!
Thanks WingedPanther!!

[WingedPanther]

No problem

[agnl666]

How would I go about saving this thread or what ever is needed to keep it accessible to me ? (I have to do the same sort of thing in class in a few weeks and I think looking this over then would help)

[WingedPanther]

It's saved on the server.