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Thread: Loop error

  1. #1
    Junior Member
    Join Date
    Nov 2013
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    Default Loop error

    I'm trying to write a loop program prompts the user to enter a number. The number has to be between 10 and 20 (both inclusive). If the number input is not between that range, it will display an error message and prompts the user to re-enter a new number again until the user get it right.

    When I enter any number between 10 and 20 it works, but when I input in a number out of the range nothing happens. Anyone know what is wrong with my code??

    import javax.swing.JOptionPane;
    public class input {
        public static void main(String[] args){
            int number;
            String input = JOptionPane.showInputDialog(null,"Enter enter a number",JOptionPane.INFORMATION_MESSAGE);
            number = Integer.parseInt(input);
            while ((number>=10)&&(number<=20))   
             if   ((number>=10)&&(number<=20))
             {   JOptionPane.showMessageDialog(null,"End of program!"); break; }  
        {JOptionPane.showMessageDialog(null,"Pls enter a number between 10 and 20","Error",JOptionPane.ERROR_MESSAGE); break;}

  2. #2
    Super Moderator
    Join Date
    Jun 2013
    So. Maryland, USA
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    Thanked 698 Times in 680 Posts

    Default Re: Loop error

    Think about how you'd do it in normal conversation:

    You: Pick a number
    Me: 5
    You: That's too low. Pick a number.
    Me: 30
    You: That's too high. Pick a number.
    Me: 15
    You: Ahhh. That's just right.

    From that, you can see that "Pick a number" is repeated, the answer is received and evaluated, and a response is generated. If the response is evaluated as out of bounds, the "Pick a number" prompt is repeated. That repetition is what must occur inside the loop. In pseudo code:
    theAnswerIsOutOfBounds = true
        // pick a number
        // evaluate the number and provide feedback
        // if the number is okay, theAnswerIsOutOfBounds = false
    } while ( theAnswerIsOutOfBounds )

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