Trying convert do-while loop to while loop

Question

I trying convert do-while to while loop and program even compile, but nothing happens. Original do-while loop code:

import java.util.Scanner;

public class CoinFlip
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(System.in);

        String coin, again;
        int flip, streak = 0;

        do
        {
            flip = 1 + (int)(Math.random()*2);

            if ( flip == 1 )
                coin = "HEADS";
            else
                coin = "TAILS";

            System.out.println( "You flip a coin and it is... " + coin );

            if ( flip == 1 )
            {
                streak++;
                System.out.println( "\tThat's " + streak + " in a row...." );
                System.out.print( "\tWould you like to flip again (y/n)? " );
                again = keyboard.next();
            }
            else
            {
                streak = 0;
                again = "n";
            }
        } while ( again.equals("y") );

        System.out.println( "Final score: " + streak );
    }
}

How it looks like after I trying to do while loop from do-while loop:

import java.util.Scanner;

public class CoinFlip2
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(System.in);

        String coin, again;
        int flip, streak = 0;
        again = keyboard.next();
        //flip = 1 + (int) (Math.random()*2);

        while ( again.equals("y") )
        {
            flip = 1 + (int) (Math.random()*2);
            if ( flip == 1)
            {
                coin = "HEADS";
            }
            else
            {
                coin = "TAILS";
            System.out.println( "You flip a coin and it is..." + coin );
            }
            if ( flip == 1)
            {
                streak++;
                System.out.println("\tThat's " + streak + " in a row....");
                System.out.print( "\tWould you like to flip again (y/n)? ");
                //again = keyboard.next();
            }
            else
            {
                streak = 0;
                again = "n";
            }
            System.out.println( "Final score: " + streak);
        }
    }
}

Code compile without problem but I see blank output after running it.

Do-While loops are guaranteed to run at least once, while loops are not. You get a blank output because you are waiting for keyboard input on line 11 — Stig Tore
– Stig Tore, Commented Nov 6, 2015 at 9:46
You can't. do-whileloops and while loops are non-interchangeable, at least without an extra Boolean variable. Why are you even trying? — user207421
– user207421, Commented Nov 6, 2015 at 9:57

Jordi Castilla · Accepted Answer · 2015-11-06 09:47:49Z

That's because you never initialize again variable to y, so it never matches condition to enter while

public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);

    String coin, again = "y";
    int flip, streak = 0;
    // flip = 1 + (int) (Math.random()*2);

    while (again.equals("y")) {
        flip = 1 + (int) (Math.random() * 2);
        if (flip == 1) {
            coin = "HEADS";
        } else {
            coin = "TAILS";
            System.out.println("You flip a coin and it is..." + coin);
        }
        if (flip == 1) {
            streak++;
            System.out.println("\tThat's " + streak + " in a row....");
            System.out.print("\tWould you like to flip again (y/n)? ");
            again = keyboard.next();
            // again = keyboard.next();
        } else {
            streak = 0;
            again = "n";
        }
    }
    System.out.println("Final score: " + streak);
    keyboard.close();
}

OUTPUT:

That's 1 in a row....
Would you like to flip again (y/n)? y
You flip a coin and it is...TAILS
Final score: 0

ParkerHalo · Accepted Answer · 2015-11-06 09:47:58Z

1

Initialize your again with "y":

String coin, again;
int flip, streak = 0;
again = "y";
...

and ask for keyboard entry in your while loop:

if ( flip == 1)
{
    streak++;
    System.out.println("\tThat's " + streak + " in a row....");
    System.out.print( "\tWould you like to flip again (y/n)? ");
    again = keyboard.next();
}

answered Nov 6, 2015 at 9:47

ParkerHalo

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2 Comments

Anonymous Over a year ago

Thanks that rocks! Is I understand correctly that if again = keyboard.next(); is commented here, then program always type "y" here for me automatically?

ParkerHalo Over a year ago

Well it won't change again at all so you'll run into an infinate loop!

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