Assignment 76; Collatz

Code

    // Donovan Rich
    // Period 6
    // Collatz Sequence
    // Collatz.java
    // 1/29/2016
    
    import java.util.Scanner;
    
    public class Collatz
    {
    	public static void main( String[] args )
    	{
    		Scanner keyboard = new Scanner(System.in);
            int num, step=0;
            do
            {
                System.out.println( "Starting number =>  " );
                num = keyboard.nextInt();
                if ( num < 1 )
                    System.out.println( "Number must be a natural number!" );
            } while ( num < 1 );
    
            while ( num != 1 )
            {
                System.out.print( num + " " );
                step++;
                if ( (num % 2) == 0 )
                    num = num/2;
                else
                    num = num*3+1;
            }
            if ( num == 1)
            {
                step++;
                System.out.println( "1 " );
            }
            System.out.println("\nIt took " + step + " steps to reach 1.");
        }
    }
        

Picture of the output