lec3.6

import java.util.Scanner;

public class DecimalToBinary {

    public static void main(String[] args) {
            Scanner in = new Scanner(System.in);
            int decimalNumber;
            String binaryNumber;
            System.out.print("Enter a positive integer: ");
            decimalNumber = in.nextInt();
            if (decimalNumber <= 0)
                  System.out.println("ERROR: entered integer is nonpositive.");
            else {
                  binaryNumber = "";
                  // algorithm step by step
                  // initial: binaryNumber = "", decimalNumber = 123
                  // step 1 : binaryNumber = "1 ", decimalNumber = 61
                  // step 2 : binaryNumber = "11 ", decimalNumber = 30
                  // step 3 : binaryNumber = "011 ", decimalNumber = 15
                  // step 4 : binaryNumber = "1011 ", decimalNumber = 7
                  // step 5 : binaryNumber = "1 1011 ", decimalNumber = 3
                  // step 6 : binaryNumber = "11 1011 ", decimalNumber = 1
                  // step 6 : binaryNumber = "111 1011 ", decimalNumber = 0
                  // stop   : (decimalNumber != 0)
                  while (decimalNumber != 0) {
                        // add spaces to separate 4-digit groups
                        if (binaryNumber.length() % 5 == 0)
                             binaryNumber = " " + binaryNumber;
                        // extract last digit in binary representation
                        // and add it to binaryNumber
                        binaryNumber = (decimalNumber % 2) + binaryNumber;
                        // cut last digit in binary representation
                        decimalNumber /= 2;
                  }
                  System.out.println("Binary: " + binaryNumber);
            }
      }