Thread: Help with calculator

Originally Posted by Norm

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.

Originally Posted by Norm

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!

Originally Posted by Norm

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");
                //}
            }
 
 
        }
    }

Originally Posted by Norm

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.

Originally Posted by Norm

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...

Sure, here's a solution to your problem. You need to split the user input into operands and the operator. Then perform the calculation based on the operator.

```java
import javax.swing.JOptionPane;
import java.util.ArrayList;

public class Calculator {
public static void main(String[] args) {
String s = JOptionPane.showInputDialog(null, "Type in expression (e.g., 2+2):");

// Split the input string into operands and operator
String[] parts = s.split("[\\+\\-\\*/]");
int num1 = Integer.parseInt(parts[0]);
int num2 = Integer.parseInt(parts[1]);
String operator = s.replaceAll("[0-9]", ""); // Extract operator from the string

int result = 0;

// Perform calculation based on the operator
switch(operator) {
case "+":
result = num1 + num2;
break;
case "-":
result = num1 - num2;
break;
case "*":
result = num1 * num2;
break;
case "/":
// Check for division by zero
if(num2 != 0)
result = num1 / num2;
else
JOptionPane.showMessageDialog(null, "Error: Division by zero");
break;
default:
JOptionPane.showMessageDialog(null, "Error: Invalid operator");
return;
}

// Display the result in a dialogue window
JOptionPane.showMessageDialog(null, "Result: " + result);
}
}
```

This code will take the input from the user, parse it into operands and operator, perform the calculation, and then display the result in a dialogue window.

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