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Thread: Help with calculator

  1. #51
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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    If you want to test if all the characters in a String are digits, use the Character class's method to test each character in a loop.

    Another way would be to test if each character is >= '0' and <= '9'
    okay we've been told to use isdigit but I don't know how to use it...
    Last edited by Dragonfly11; November 6th, 2019 at 10:02 AM.

  2. #52
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    Default Re: Help with calculator

    Here is how you use a static method:
    returnValue = TheClassName.theMethodName(theArgs);

    Read the API doc for specifics: http://docs.oracle.com/javase/8/docs/api/index.html
    If you don't understand my answer, don't ignore it, ask a question.

  3. #53
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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    Here is how you use a static method:
    returnValue = TheClassName.theMethodName(theArgs);

    Read the API doc for specifics: http://docs.oracle.com/javase/8/docs/api/index.html
    okay thank you like this?
    returnValue = TheClassName.theMethodName(tal1);
    Last edited by Dragonfly11; November 6th, 2019 at 11:14 AM.

  4. #54
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    Default Re: Help with calculator

    Did you try it? What happened?
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    Did you try it? What happened?
    No it doesn't work, I try doing it with a for loop with isdigit in it
    for (int i = 0; i <s.length() ; i++) {
    char a4 = s.charAt(i);
    if (!Character.isDigit(a4)) {
    JOptionPane.showMessageDialog(null, "you need to use numbers");
    System.exit(0);
    }

    }
    it shows error message but when I try to write 1+1 it also display the error message.

  6. #56
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    Default Re: Help with calculator

    No it doesn't work
    Please post the full code so we can see what it is doing.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    Please post the full code so we can see what it is doing.

       String tal1 = "";
            String tal2 = "";
     
            String s = JOptionPane.showInputDialog("Skriv in tal");
     
     
            if (s.isEmpty()) {
                JOptionPane.showMessageDialog(null, "Får inte vara tomt");
            }
            if (s.contains("%")) {
                JOptionPane.showMessageDialog(null, "Får inte innehålla %");
     
            }
            if (s.contains(" ")) {
                JOptionPane.showMessageDialog(null, "Hittar ingen operator");
            }
            if ((s.startsWith("+")) || (s.startsWith("-")) || (s.startsWith("*")) || (s.startsWith("/"))) {
                System.out.println("error start with");
                System.exit(0);
            }
            if ((s.endsWith("+")) || (s.endsWith("-")) || (s.endsWith("*")) || (s.endsWith("/"))) {
                System.out.println("error end with");
                System.exit(0);
            }
     
     
            int count = 0;
     
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '*' || s.charAt(i) == '/' || s.charAt(i) == '+' || s.charAt(i) == '-') {
     
     
                    count++;
                }
     
            }
            if (count > 1) {
                System.out.println("error");
                System.exit(0);
            }
            for (int i = 0; i < s.length(); i++) {
                char a4 = s.charAt(i);
                if (!Character.isDigit(a4)) {
                    JOptionPane.showMessageDialog(null, "Du behöver använda dig av siffror");
                    System.exit(0);
     
                    if (s.contains("*")) {
                        int tal = s.indexOf("*");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2); //error
                        double result = (resultat * resultat2);
                        //System.out.println(result);
                        JOptionPane.showMessageDialog(null, Math.round(result));
     
                    } else if (s.contains("+")) {
                        int tal = s.indexOf("+");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2);
                        double result = (resultat + resultat2);
                        System.out.println(result);
                        JOptionPane.showMessageDialog(null, Math.round(result));
     
                    } else if (s.contains("-")) {
                        int tal = s.indexOf("-");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2);
                        double result = (resultat - resultat2);
                        System.out.println(result);
                        JOptionPane.showMessageDialog(null, Math.round(result));
     
     
                    }
                    if (s.contains("/0")) {
                        JOptionPane.showMessageDialog(null, "Det finns ingen operator");
     
                    } else if (s.contains("/")) {
                        int tal = s.indexOf("/");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2);
                        double result = (resultat / resultat2);
                        System.out.println(result);
                        JOptionPane.showMessageDialog(null, result);
                    }
     
                    //} else {
                    //JOptionPane.showMessageDialog(null, "input error");
                    //}
                }
     
     
            }
        }
    thank you so much!

  8. #58
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    Default Re: Help with calculator

    The posted code is missing the import statements and the declaration of the class.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    The posted code is missing the import statements and the declaration of the class.
    you mean these?
    package com.company;

    import javax.swing.*;

    public class Main {

    public static void main(String[] args) {

    sorry for not including them

    --- Update ---

    package com.company;
     
    import javax.swing.*;
     
    public class Main {
     
        public static void main(String[] args) {
            String tal1 = "";
            String tal2 = "";
     
            String s = JOptionPane.showInputDialog("Skriv in tal");
     
     
            if (s.isEmpty()) {
                JOptionPane.showMessageDialog(null, "Får inte vara tomt");
            }
            if (s.contains("%")) {
                JOptionPane.showMessageDialog(null, "Får inte innehålla %");
     
            }
            if (s.contains(" ")) {
                JOptionPane.showMessageDialog(null, "Hittar ingen operator");
            }
            if ((s.startsWith("+")) || (s.startsWith("-")) || (s.startsWith("*")) || (s.startsWith("/"))) {
                System.out.println("error start with");
                System.exit(0);
            }
            if ((s.endsWith("+")) || (s.endsWith("-")) || (s.endsWith("*")) || (s.endsWith("/"))) {
                System.out.println("error end with");
                System.exit(0);
            }
     
     
            int count = 0;
     
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '*' || s.charAt(i) == '/' || s.charAt(i) == '+' || s.charAt(i) == '-') {
     
     
                    count++;
                }
     
            }
            if (count > 1) {
                System.out.println("error");
                System.exit(0);
            }
            for (int i = 0; i < s.length(); i++) {
                char a4 = s.charAt(i);
                if (!Character.isDigit(a4)) {
                    JOptionPane.showMessageDialog(null, "Du behöver använda dig av siffror");
                    System.exit(0);
                }
     
     
                    if (s.contains("*")) {
                        int tal = s.indexOf("*");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2); //error
                        double result = (resultat * resultat2);
                        //System.out.println(result);
                        JOptionPane.showMessageDialog(null, Math.round(result));
     
                    } else if (s.contains("+")) {
                        int tal = s.indexOf("+");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2);
                        double result = (resultat + resultat2);
                        System.out.println(result);
                        JOptionPane.showMessageDialog(null, Math.round(result));
     
                    } else if (s.contains("-")) {
                        int tal = s.indexOf("-");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2);
                        double result = (resultat - resultat2);
                        System.out.println(result);
                        JOptionPane.showMessageDialog(null, Math.round(result));
     
     
                    }
                    if (s.contains("/0")) {
                        JOptionPane.showMessageDialog(null, "Det finns ingen operator");
     
                    } else if (s.contains("/")) {
                        int tal = s.indexOf("/");
                        tal1 = s.substring(0, tal);
                        tal2 = s.substring(tal + 1);
                        System.out.println("tal " + tal1);
                        System.out.println("tal " + tal2);
                        double resultat = Double.parseDouble(tal1);
                        double resultat2 = Double.parseDouble(tal2);
                        double result = (resultat / resultat2);
                        System.out.println(result);
                        JOptionPane.showMessageDialog(null, result);
                    }
     
                    //} else {
                    //JOptionPane.showMessageDialog(null, "input error");
                    //}
                }
     
     
            }
        }

  10. #60
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    Default Re: Help with calculator

    There is a lot of repeated code that should be in a method.
    The test using isDigit should be in a method that is passed the Strings: tal1 and tal2 one at a time to test if they are valid numbers.

    In my first post I said this:
    Before writing any more code you need to do some design work laying out the steps the program needs to take to solve the problem.
    Once you have the steps, then try writing the code to implement the steps.
    The program has lots of problems in it. You need to work out the steps it should take to solve the problem, before writing the code. The code has most of the coding techniques that are needed, but they are not used in a logic way.
    If you don't understand my answer, don't ignore it, ask a question.

  11. #61
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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    There is a lot of repeated code that should be in a method.
    The test using isDigit should be in a method that is passed the Strings: tal1 and tal2 one at a time to test if they are valid numbers.

    In my first post I said this:


    The program has lots of problems in it. You need to work out the steps it should take to solve the problem, before writing the code. The code has most of the coding techniques that are needed, but they are not used in a logic way.
    I see but I don't know how....and I don't have much time left on this assignment I have to deliver it tomorrow.

  12. #62
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    Default Re: Help with calculator

    Here is a sample design:
    get user input into a string
    find the operator that should be in the middle of the string -> if not found give error and exit
    split the string into three parts: first operand, operator, second operand
    check that first operand is a valid number (write method for this) -> if not give error
    check that second operand is a valid number (write method for this) -> if not give error
    convert first operand to an int value
    convert second operand to an int value, check if /0
    use the operator to compute the result using the two int values
    show result to user
    If you don't understand my answer, don't ignore it, ask a question.

  13. #63
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    Default Re: Help with calculator

    Quote Originally Posted by Norm View Post
    Here is a sample design:
    get user input into a string
    find the operator that should be in the middle of the string -> if not found give error and exit
    split the string into three parts: first operand, operator, second operand
    check that first operand is a valid number (write method for this) -> if not give error
    check that second operand is a valid number (write method for this) -> if not give error
    convert first operand to an int value
    convert second operand to an int value, check if /0
    use the operator to compute the result using the two int values
    show result to user
    Okay I see, I feel like I've done that (or at least tried...) but made a really bad code for it....I did manage to fix my problem with a isLetter statement. The problem I have now is that it prints out the input say if you write 1+1, you get a message dialogue 3 times and also in the terminal.
    }if (Character.isLetter(s.charAt(i))){
    System.out.println("error");
    System.exit(0);
    }

    Also Thank you very much for trying to help me I reall appreciate it. It's just a very hard assignment...

  14. #64
    Super Moderator Norm's Avatar
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    Default Re: Help with calculator

    My suggestion is to start over and follow a design for the steps the program should take. Trying to fix what you have now will be harder than writing a new program from the beginning. The current program has most of the needed techniques, but they are not organized correctly.
    If you don't understand my answer, don't ignore it, ask a question.

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