I was doing my 2nd assignment to create a bank program using Java.
I got a problem when I run a few times.

For example, I entered the starting amount as $50000.
Then, I choose withdraw. I tried to enter withdrawal amount as $5000.
Then, I choose to check balance, and it says $50000 instead of $45000.

If someone check the code whether there is a problem.

package sean_lab2;

import javax.swing.*;

public class Sean_LAB2 
{
    public static void main (String[] args) 
    {
        double bal; // Balance of savings account
        int sel = 0; // Menu selection

        bal = Double.parseDouble(JOptionPane.showInputDialog(null, "Enter your starting amount (in $):", "Enter starting amount", JOptionPane.QUESTION_MESSAGE));

        while (sel != 4)
        {
            sel = Integer.parseInt(JOptionPane.showInputDialog(null, "Select an option: \n" + 
                    "1. Withdraw \n" + 
                    "2. Deposit \n" + 
                    "3. Check balance \n" + 
                    "4. Exit" ));

            switch(sel)
            {
                case 1: 
                    withdraw(bal);
                    break;

                case 2:
                    deposit(bal);
                    break;

                case 3:
                    CheckBalance(bal);
                    break;

                default:
                    JOptionPane.showMessageDialog(null, "Thank you for using the program.");
                    System.exit(0);
            }
        }
    }

    public static double withdraw (double bal)
    {
        double withdrawAmt; // Amount to withdraw

        withdrawAmt = Double.parseDouble(JOptionPane.showInputDialog(null, "Enter amount to withdraw (in $):", "Withdraw", JOptionPane.QUESTION_MESSAGE));

        while (bal < withdrawAmt)
        {
            JOptionPane.showMessageDialog(null, "The amount you've entered to withdraw is more than your savings balance.\nPlease re-enter.", "Withdraw", JOptionPane.ERROR_MESSAGE);
            withdrawAmt = Double.parseDouble(JOptionPane.showInputDialog(null, "Enter amount to withdraw (in $):", "Withdraw", JOptionPane.QUESTION_MESSAGE));
        }
        bal -= withdrawAmt;
        return bal;
    }

    public static double deposit (double bal)
    {
        double depositAmt; // Amount to deposit

        depositAmt = Double.parseDouble(JOptionPane.showInputDialog(null, "Enter amount to deposit (in $):", "Deposit", JOptionPane.QUESTION_MESSAGE));

        while (depositAmt <= 0)
        {
            JOptionPane.showMessageDialog(null, "The amount you've entered to deposit is a negative amount or zero.\nPlease re-enter.", "Deposit", JOptionPane.ERROR_MESSAGE);
            depositAmt = Double.parseDouble(JOptionPane.showInputDialog(null, "Enter amount to deposit (in $):", "Deposit", JOptionPane.QUESTION_MESSAGE));
        }
        bal += depositAmt;
        return bal;
    }

    public static void CheckBalance (double bal)
    {
        JOptionPane.showMessageDialog(null, "Your balance is: $" +bal, "Check Balance", JOptionPane.INFORMATION_MESSAGE);
    }

}

If you want to fix the problem then yes, of course, you will have to change the code.

Yourr methods are designed to take the old balance as a parameter and return the new balance. Right now you are ignoring the new balance that's returned. You need to asssign that new value to the bal variable (declared on line 9).

i think all you need is to define your "bal" outside of your main as "public double bal" that way the rest of your code has access to change that value. Right now your other methods have no way of accessing "bal". Side note why do your methods return "bal"? Is this how you are setting "bal" from the method? If so i have never seen a return implemented this way.

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