Question

The problem is that I keep getting the balance to be minus, it executes the part where the money needs to be taken out, but the ‘if’ statement that I’ve put in place should prevent that. I’m new to programming, I’m very sorry if this is silly.

Here is my main:

public class PrinterAccount
{
    private int balance;

    public void topUp(int amount)
    { 
        balance += amount;
    }
    public int getBalance()
    { 

        return balance;
    }
    public boolean printDocument(int numPages, boolean isDoubleSided)
    {

        if (isDoubleSided)
        {
            if(numPages % 2 == 0)
            {
                int b = 0;
                b = b - ((numPages/2)*5);
                    if (balance > b)
                    {
                        balance -= ((numPages/2) * 5);
                        return true;
                    }
                    else
                    {
                        return false;
                    }
            }
            else
            {
                numPages = numPages + 1;
                int a = 0;
                a = a - ((numPages/2)*5);
                    if (balance > a)
                    {
                        balance -= ((numPages/2) * 5);
                        return true;
                    }
                    else
                    {
                        return false;
                    }
            }
        }
        else
        {
            int c = 0;
            c = c - (numPages*5);
                if (balance > c)
                {
                    balance -= (numPages*5);
                    return true;
                }
                else
                {
                    return false;
                }

        }   
    }
}

and here is my test:

public class PrinterAccountTest
{
    public static void main(String[] args)
    {
        // Create an object of class PrinterAccount
        PrinterAccount myprinterAccount = new PrinterAccount();
        // Add 10 pounds credit (1000 pence)
        myprinterAccount.topUp(1000);

        // **************TEST 1************************
        // Print a 15-page document, single-sided, should cost 75p
        boolean res = myprinterAccount.printDocument(15, false);
        // The document should have printed successfully
        if (res)
            System.out.println("The document printed successfully");
        else
            System.out.println("The document failed to print: not enough credit.");
        // Display the remaining balance: should be 925
        System.out.println("Remaining balance is " + myprinterAccount.getBalance());

        // **************TEST 2************************
        // Print a 20-page document (even number of pages), double-sided, should cost 50p
        res = myprinterAccount.printDocument(20, true);
        // The document should have printed successfully
        if (res)
            System.out.println("The document printed successfully");
        else
            System.out.println("The document failed to print: not enough credit.");
        // Display the remaining balance: should be 875
        System.out.println("Remaining balance is " + myprinterAccount.getBalance());

        // **************TEST 3************************
        // Print a 7-page document (odd number of pages), double-sided, should cost 20p
        res = myprinterAccount.printDocument(7, true);
        // The document should have printed successfully
        if (res)
            System.out.println("The document printed successfully");
        else
            System.out.println("The document failed to print: not enough credit.");
        // Display the remaining balance: should be 855
        System.out.println("Remaining balance is " + myprinterAccount.getBalance());

        // **************TEST 4************************
        // Print a 200-page document, single-sided, should cost 1000p
        res = myprinterAccount.printDocument(200, false);
        // Should get a message saying the document failed to print
        if (res)
            System.out.println("The document printed successfully");
        else
            System.out.println("The document failed to print: not enough credit.");
        // Display the remaining balance: should be 855
        System.out.println("Remaining balance is " + myprinterAccount.getBalance());


    }
}

This is the result I get when I run the code:

The document printed successfully
Remaining balance is 925
The document printed successfully
Remaining balance is 875
The document printed successfully
Remaining balance is 855
The document printed successfully
Remaining balance is -145

But I need it to display:

The document printed successfully
Remaining balance is 925
The document printed successfully
Remaining balance is 875
The document printed successfully
Remaining balance is 855
The document failed to print: not enough credit.
Remaining balance is 855

Answer 1

This lines in the print document method:

    int c = 0;
    c = c - (numPages*5);
    if (balance > c) ...

Variable c will always have negative value. I suppose you wanted to add (numPages*5) instead of subtracting it.