/**
 * This simple tool allows you to convert numbers from base 2 to base 10
 * (decimal numeral system) or from base 10 to base 2 (binary).
 *
 * @author Ciprian Borundel
 *
 */

import java.util.Scanner;


public class NumberBases {

	public static StringBuilder sb = new StringBuilder();
	public static Scanner scan = new Scanner(System.in);

	public static String convertNumberToBase2(int n) {
		while (n > 0) {
			sb.append(n % 2);
			n /= 2;
		}
		sb.reverse();
		String convertedNumber = sb.toString();
		return convertedNumber;
	}

	public static int convertNumberToBase10(String number) {
		int pow = 0, sum = 0;
		for (int i = number.length() - 1; i >= 0; i--) {
			if (Character.isDigit(number.charAt(i)) &&
				Character.getNumericValue(number.charAt(i)) < 2) {
				sum += Character.getNumericValue(number.charAt(i)) * (Math.pow(2, pow));
				pow++;
			} else {
				return 0;
			}
		}
		return sum;
	}

	public static void main(String[] args) {
		System.out.println("1. Convert number from base 2 to base 10");
		System.out.println("2. Convert number from base 10 to base 2");
		int n = scan.nextInt();
		if (n == 1) {
			System.out.println("Enter number in base 2:");
			System.out.println(convertNumberToBase10(scan.next()));
		} else if (n == 2) {
			System.out.println("Enter number in base 10:");
			System.out.println(convertNumberToBase2(scan.nextInt()));
		} else {
			System.out.println("Invalid option!");
		}

	}
}