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Thread: Java while loops and switches

  1. #1
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    Default Java while loops and switches

    Hi,
    I'm a beginner at Java programming and I was wondering if anyone could help / explain how to use a while loop in a task. The task is to create a menu which is appears constantly after the user has made an input. The user should enter instructions in the form of the numbers 1 to 4 as follows:
    1 - Reroll the dice
    2-get the value
    3-show maximum
    4-show minimum
    Once the user has entered a number and an instruction is made the menu must re-appear asking the user to make a choice again. This must happen repeatedly
    Example:
    User enters: 4
    Program displays: "The minimum value is: n"
    Then the menu reappears asking the user to make another choice
    I understand I need to use a while loop (and maybe a switch) but I’m unsure how to make this happen.
    I'm not really good at explaining things so I apologize if anything is unclear or just confusing.


  2. #2
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    Default Re: Java while loops and switches

    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java while loops and switches

    You need to make an attempt and write some code. When you get stuck post the code here using code tags. Include full error messages. Ask a specific question.
    Improving the world one idiot at a time!

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    Default Re: Java while loops and switches

    //Asks the user to input a number for dices sides
    System.out.println("How many sides should the dice have?") ;
    int numberOfSides ;
    Scanner scanner = new Scanner (System.in);
    numberOfSides = scanner.nextInt() ;
    Dice2 d= new Dice2 (numberOfSides);
     
    // The user can only enter 4,6,8,12,20 or 100
    //Any other number should terminate the program
    if ( numberOfSides == 4 || numberOfSides == 6 || numberOfSides == 8 || numberOfSides == 12 ||numberOfSides == 20 ||numberOfSides == 100 ){
    [B]once the number of sides is declared this menu should appear [/B]
    System.out.println("Please make a choice:") ;
    System.out.println("1 - reroll the dice") ;
    System.out.println("2 - get the value") ;
    System.out.println("3 - show the maximum") ;
    System.out.println("4 - show the minimum") ;
    } else {
    System.exit(0);
    } // closing else statement
     
    //Storing the users choice and current value of the dice
    int choice ;
    choice = scanner.nextInt() ;
    int currentValue;
    currentValue = d.getValue() ;
     
    [B]This is suppose to be a while loop which makes the menu re-appear after the user has made a choice[/B]
    while (choice == 1 || choice == 2 || choice == 3 || choice == 4) {
    System.out.println("Please make a choice:") ;
    System.out.println("1 - reroll the dice") ;
    System.out.println("2 - get the value") ;
    System.out.println("3 - show the maximum") ;
    System.out.println("4 - show the minimum") ;
    choice++;
     
    //after the user enters a choice either one of the cases become true... any other number should terminate the program
    switch (choice) {
    case 1: d.reroll();
    break;
    case 2: System.out.println("The current value is " + currentValue);
    break;
    case 3: int maximum = Math.max(currentValue, numberOfSides);
    break;
    case 4: int minimum = Math.min(currentValue, numberOfSides);
    System.out.println("The minimum is " + minimum) ;
    break;

    I did make a loop using the if statement however after submitting the lectures feedback was not to use to many if statements

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    Default Re: Java while loops and switches

    Ok, well this might get messy, but it might also help you find the problem yourself. For each line of code in your main, add a comment which explains the purpose of the line. It sounds to me like you've made a logic mistake somewhere, so following this strategy might allow you to find your mistake.
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    Default Re: Java while loops and switches

    Please edit your post and wrap your code with code tags:
    [code=java]
    YOUR CODE HERE
    [/code]
    to get highlighting and preserve formatting.

    The code needs to test that the user has entered a valid response.
    You could use an if statement
    or have a default: case in the switch statement.


    BTW You should ALWAYS code a default case in a switch to catch any unexpected values and print out a message saying the value was unexpected.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java while loops and switches

    while (condition) {
    statement;
    }

    Basically if the condition is true then the statements are executed until the condition becomes false.

    Example:

    int num = 5;
    while (num <= 5) {
    num++;
    System.out.println("*");
    }
    5 is smaller than 5 4 times and equal to 5 once. This means the statement will be executed 5 times.

    Scanner scan = new Scanner (System.in);
    String example;
    System.out.print("Enter a word: ");
    example = scan.nextLine();
     
    switch (example) {
     
    case "no":
    System.out.println("This is just an example.");
    break;
     
    case "yes":
    System.out.println("This is just an example.");
    break;
    }

    So basically it will execute the tasks of the case matched.

    Edit: you can also use default while using the switch (basically means anything but the above cases).

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    Default Re: Java while loops and switches

    This means the statement will be executed 5 times.
    @D.K Did you test that code? How many times did the execute the statement in loop?


    you can also use default
    You should ALWAYs use the default to catch unexpected input.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java while loops and switches

    Quote Originally Posted by Norm View Post
    @D.K Did you test that code? How many times did the execute the statement in loop?



    You should ALWAYs use the default to catch unexpected input.
    Opps, forgot that was an infinite loop XD.

    Edit: if you add num++; in the while loop that will fix the infinite loop (increments num by 1 each time).

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    Default Re: Java while loops and switches

    Quote Originally Posted by D.K View Post
    Opps, forgot that was an infinite loop XD.
    Not an infinite loop either. It will execute once, num is 5 which is <= 5, enters loop, increments to 6 which is no longer <= 5 exits loop.
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