Problem with adding totals from user selected CheckBoxes-CodePudding

I am creating a form that allows the user to select from a group of checkboxes for automotive services. In the form, the user selects from a list of priced services and a final total is calculated based on what is selected.

The logic of the selected services being added up is placed within a method that returns the total.

photo of form .

Once the user clicks on the calculate button, all selected prices will be added up and displayed by the total fees label.

    public partial class Automotive_Shop : Form
    {
        const int salesTax = (6 / 100);
        // prices for services
        const int
            oilChange = 26,
            lubeJob = 18,
            radiatorFlush = 30,
            transissionFlush = 80,
            inspection = 15,
            mufflerReplacement = 100,
            tireRotation = 20;

        int total = 0;

        public Automotive_Shop()
        {
            InitializeComponent();
        }




        private int OilLubeCharges()
        {
            if (oilChangeCheckBox.Checked == true)
            {
                total  = oilChange;
            }                 
            if (lubeJobCheckBox.Checked == true)
            {
                total  = lubeJob;
            }
          
            return total;
        }
           
      

      


        private void calculateButton_Click(object sender, EventArgs e)
        {
            totalFeesOutput.Text = OilLubeCharges().ToString("C");
                
        }

        private void exitButton_Click(object sender, EventArgs e)
        {
            // close application
            this.Close();
        }
    }

The total should only be added once.

For instance: if the "oil change" check box is selected, then the total should be $26.

if the "lube job" check box is selected, then the total should be $18.

And if both check boxes are selected, then the total should be $44.

What ends up happening is that after the first check box is selected and the calculate button is clicked, the "total" variable value continues to be added up.

So if i select "oil change" then click calculate, I get $26. if I deselect it and select "lube job" the total doesn't equal $18, but $44.

CodePudding user response：

To fix this problem, the total variable needs to be reset to 0 before the calculation happens.

The calculate button click event should be updated to look like this:

private void calculateButton_Click(object sender, EventArgs e)
{
    total = 0;
    totalFeesOutput.Text = OilLubeCharges().ToString("C");
}

CodePudding user response：

A function should be responsible for whatever it does. So everything it does should be there, nothing more and nothing less.

This means when a member function is calculating a total, and in the comments you refer to it as a subtotal, this is what the function should do.

Therefore you declare in that function int subtotal = 0; and return that.

Then you could store this to a member variable if you like.

As an example regarding your comments, I have added the member function int ApplyDiscount(...).

The only thing it does is applying a discount to 'a' subtotal you pass in. It should be improved for a working application.

At the button click the OilLubeCharges are calcultated, then that is passed into ApplyDiscount.

This return value you could store at a global variable. Both you could to event specify the full cost, the discount in price and the total.

        // Added a functionality due to the comments
        // When `discount` is 0.2f for 20%
        private int ApplyDiscount(int subtotal, float discount)
        {
            return (int)( subtotal - ( subtotal * discount ) );
        }

        private int OilLubeCharges()
        {

            int subtotal = 0;

            if (oilChangeCheckBox.Checked == true)
            {
                subtotal  = oilChange;
            }                 
            if (lubeJobCheckBox.Checked == true)
            {
                subtotal  = lubeJob;
            }
          
            return subtotal;

        }

        ...

        private void calculateButton_Click(object sender, EventArgs e)
        {

            int subtotal = OilLubeCharges();
            int total = ApplyDiscount(subtotal, 0.2f);

            totalFeesOutput.Text = total.ToString("C");
                
        }