How to convert numbers to binary and hex (without built-in functions)?

Question

Since this is homework, I can't use built-in functions. I have to use algorithms in Java.

This is what I have so far but it is wrong.

import java.util.Scanner;

public class ChangingFigures {
    public static void main (String[] args){
        Scanner scanner = new Scanner (System.in);
        System.out.print("Enter an integer between 0 and 127:");

        int num = scanner.nextInt ();

        String hex = Integer.toHexString(num);
        String bin = Integer.toBinaryString(num); 
        // ...
    }
}

seems to work fine for me, what problem are you running into? — Hunter McMillen
– Hunter McMillen, Commented Jun 21, 2011 at 13:32

Alnitak · Accepted Answer · 2011-06-21 13:33:39Z

7

The algorithm is trivial:

make an empty string
do:
    prepend "n" modulo "base" to that string
    divide "n" by "base"
until (n == 0)

if "base" is greater than 10 you'll need to do a little work to convert the "digits" into the letters that represent 10+

answered Jun 21, 2011 at 13:33

Alnitak

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4 Comments

Ken White Over a year ago

+1 for providing pseudocode instead of just giving the answer (as well as the algo being right, of course). Very nicely done.

JAB Over a year ago

While it doesn't matter since user808520 seems to be using Java, the div function in the C standard library would actually be pretty nice for this sort of thing, as it allows you to calculate the modulo value in the same step as the division.

Alnitak Over a year ago

@JAB yes, if performance were an issue then calculating the division and remainder at the same time would be optimal.

JAB Over a year ago

Well, there's that, but I was speaking more generally. It's not just the performance but the way the code looks. On the other hand the usage of div could potentially be confusing to those who don't know the standard library that well, so it's still a tradeoff despite the advantages.

ninja · Accepted Answer · 2011-06-21 13:43:03Z

-1

To HEX:

String HEXES = "0123456789ABCDEF";
System.out.println(HEXES.charAt((num & 0xF0) >> 4) + "" + HEXES.charAt((num & 0x0F)));

To binary

answered Jun 21, 2011 at 13:43

ninja

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1 Comment

Atreys Over a year ago

your magic-looking answer seems to be missing something, and doesn't get at the algorithm, or explain anything. if num is 256 it fails greatly.

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