Decimal to binary, octal to decimal

[matejm1994]

Hello to all!

I am new on this forum, and I am quite new to Java too. I am from Slovenia, and I don't speak English very well, so please excuse me for mistakes.

Ok, for homework I have to write a program, which convert from decimal to binary and than another program, which convert from octal to decimal.
In the program which convert from decimal to binary, I have to use while loop, and this is a problem. I know how to do it with toBinaryString(), but I don't have idea, how to do it with While loop.

So, write this program, to convert from decimal to binary. The Binary number is save in variable a, but I have no Idea how to revese it. Now, the (Decimal) 55 = (Binary)111011, but it is wrong, it have to be 110111. How can I reverse this number?

import java.util.*;

public class Convert
{

    public static void main(String[] args)
    {
	Scanner in = new Scanner(System.in);
	
	System.out.println("Input decimal number: ");
	int dec = in.nextInt();
	
	int udec = dec;
	int ost;
	String a = new String();
	
	
	while (udec >= 1)
	{
	    ost = udec % 2;
	    
	    a = ost + "";
	    udec /=2;
	    System.out.print(a);
	}
	
    }
}

And now, I have got another question. I have no Idea, how to convert from Octal to Decimal. In this case isn't necessarily to use While loop, I should use any of method, if they exists. :) But it is to complicated for me, so, if you have any idea, i will be happy.

Thanks to all!

[Fubarable]

Octal to decimal conversion is easy. Please have a look here: Octal - Wikipedia, the free encyclopedia

Also, Integer has a method, toOctalString and parse that will help. Your best way to learn these methods is to play with them with different numbers and Strings and see what happens.

[JavaHater]

decimal to binary

import java.util.Scanner;
public class decToBinary {
        public static void main(String[] args ){
                StringBuilder str = new StringBuilder();
                System.out.printf("Enter a decimal number: ");
                int number=0;
                Scanner input = new Scanner ( System.in );
                number = input.nextInt();
                while( number > 1){
                        number = number / 2;
                        str.append ( (number % 2 == 0) ? 0 : 1 );
                }
                str.insert(0,0);
                System.out.println("str: " + str.reverse().toString() );
        }
}

octal to decimal

import java.util.Scanner;
public class octToDecimal {
        public static void main(String[] args ){
                System.out.printf("Enter an octal number: ");
                String number;
                Scanner input = new Scanner ( System.in );
                number = input.nextLine();

                // store values from 1, 8, 64 ....
                // if number input is 100 for example, then octals array will contain 1,8,64
                int[] octals = new int[number.length() ];
                octals[0]=1;
                for (int i = 1;i< number.length() ;i++){
                        octals[i] = octals[i-1] * 8;
                }

                int j = 0;
                int sum=0; // add up each position
                for (int i = number.length()-1 ; i>=0 ;i--){
                        // starting from end of the string
                        char c = number.charAt(i) ;
                        // accumulate the sum
                        sum += Character.digit(c,10) * octals[j] ;
                        j++;
                }
                System.out.println("Decimal value for "+ number + " is: " + sum );

        }
}

[matejm1994]

Thanks to both of you :)
Fubarable, thanks for link. Now, I understand this convert :P Now, I have to play with all this metods, just you say.

JavaHater, woo, thanks for all. You made my dam brighter :D Really, really thanks for this. (I will not just copy-paste it to my homework, but I will try to understand it, so I hope, I will learn something new)

BTW, this forum is great