Convert a number from base 10 to N

Question

This code is a part of a project that I have to develop. I need to write a java method that converts a number (base 10) to another number in n base. This is the code of the class:

public class converter {

    public int from_10_to_n(int base, int newbase) {

       int k = 0;
       String res = "";
       String output = "";

       do {                        //Below I explain what I'm doing here
        base /= newbase;   
        k = base % newbase;
        res += String.valueOf(k);
       } while (base != 0);

       for(int i=res.length()-1; i>-1; i--) {
        output += res.charAt(i);
       }

       return Integer.parseInt(output);
    }

I thought to make the program in this way:

The do {} while(); loop divides the numbers and saves in k the remainders. Then I make a for loop that reverses the string res (which has the reminders).

By the way when I call the method in my main, I am missing the last digit. I mean:

converter k = new converter();
int e = k.from_10_to_n(a /*base 10 number*/, b /*Base n number*/);

System.out.println(a+" -> "+b+" is " + e);

With this code, if I want to convert 231 to base 4 I have 321 as result instead of 3213. I have checked my code but I cannot find a solution. Any idea?

I have the same error with other bases. For example 31 (base 10) is 11111 (base 2) but my program returns 1111.

Answer 1

Flip the order of the first 2 lines in the loop; by doing the division first, you lose the first remainder. But then you'll need to handle the last remainder.

Answer 2

The problem lies here:

base /= newbase;
k = base % newbase;

Try this with some real numbers, like 231 and base 4 in your example.

base /= newbase

Now base is 57 and your k will be incorrect. You should get the remainder first, then divide:

k = base % newbase;
base /= newbase;

There are also some style problems with your code which you should consider correcting:

• base doesn't really hold any base, just input value - maybe rename it to input or something like that?
• Mixed indentation. Your loops are indented with one space, while the rest of the code has four.