Convert binary to decimal with an array

Question

Im trying to make a binary string into a decimal. It will terminate if -1 is entered. I am stuck with using an array. It was suggested to use: public static int binaryToDecimal (String binaryString) . But Im not sure how to do that. This is what I have:

import java.util.Scanner;

public class BinaryConversion {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        String inString;
        int decimal;

        System.out.println("Enter a binary number: ");
        inString = input.nextLine();

        while (inString != "-1") {
            int i;
            int binaryLength;

            binaryLength = inString.length();

            for (i = 0, decimal = 0; i < binaryLength; i++) {
                decimal = decimal * 2 + (inString[i] - 0);
                System.out.print(decimal);

            } 
            System.out.println("Enter a binary number: ");
            inString = input.nextLine();
        }
        System.out.println("All set !");
    }
}

It says there is a compilation problem with the array. Thank you!

Alex Yuly · Accepted Answer · 2014-03-26 01:00:02Z

1

inString is a String, not an array. So, you can't use inString[i]. To get the character at a given position in the string, use inString.charAt(i), which returns a char.

Then, you'll also have to convert that char into an int. You can do this with Character.getNumericValue(char).

So in summary, instead of

inString[i]

you need to use

Character.getNumericValue(inString.charAt(i))

answered Mar 26, 2014 at 1:00

Alex Yuly

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Comments

user840718 · Accepted Answer · 2014-03-26 01:05:57Z

Try this one:

        public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        String inString;
        int decimal;

        System.out.println("Enter a binary number: ");
        inString = input.nextLine();
        //Character.getNumericValue(inString.charAt(i))

        while (inString != "-1") {
            int i;
            int binaryLength;

            binaryLength = inString.length();

            for (i = 0, decimal = 0; i < binaryLength; i++)
            {
                decimal = decimal * 2 + (Character.getNumericValue(inString.charAt(i)) - 0);
                System.out.print(decimal);

            } 
            System.out.println("Enter a binary number: ");
            inString = input.nextLine();
        }
        System.out.println("All set !");
    }

}

As suggested, you have to use Character.getNumericValue

Florent Bayle · Accepted Answer · 2014-03-26 01:14:36Z

1

You can simplify the code by using Integer.parseInt():

public static void main(String[] args) {
    final Scanner input = new Scanner(System.in);

    String inString;

    while (true) {
        System.out.println("Enter a binary number: ");
        inString = input.nextLine();

        if (inString.equals("-1"))
            break;

        System.out.println(Integer.parseInt(inString, 2));
    }
    System.out.println("All set !");
}

answered Mar 26, 2014 at 1:14

Florent Bayle

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Comments

libik · Accepted Answer · 2014-03-26 01:03:59Z

You had few logical and few syntax errors.

This is working code :

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);

    String inString;
    int decimal;

    System.out.println("Enter a binary number: ");
    inString = input.nextLine();

    while (!"-1".equals(inString)) {
        int i;
        int binaryLength;

        binaryLength = inString.length();

        for (i = binaryLength-1, decimal = 0; i >= 0; i--) {
            if (inString.charAt(i) == '1') {
                decimal += Math.pow(2, binaryLength-i-1);
            }
        }
        System.out.println(decimal);

        System.out.println("Enter a binary number: ");
        inString = input.nextLine();
    }
    System.out.println("All set !");
}

Note that comparing String cannot be done with ==, you have to use equals or compareTo methods.

David · Accepted Answer · 2017-06-29 21:37:07Z

0

byte[] binary = {1,1,0,1};

int decimal = 0;
for(int i=binary.length-1, j=0; i>=0; i--, j++){
    decimal  += binary[i]*Math.pow(2, j);
}

answered Jun 29, 2017 at 21:37

David

1

2 Comments

avojak Over a year ago

OP will be starting with a String, not a byte[].

Toby Speight Over a year ago

Thank you for this code snippet, which may provide some immediate help. A proper explanation would greatly improve its educational value by showing why this is a good solution to the problem, and would make it more useful to future readers with similar, but not identical, questions. Please edit your answer to add explanation, and give an indication of what limitations and assumptions apply.

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