c# using multiple listbox

Question

I have 2 ListBoxes and 2 TextBoxes, what I need it to do is if I click an item in list box 1 it shows 2 or more items in list box 2 and if I click an item in list box 2 there will be an operation and it will appear in text box 1 and text box 2, ex. ballpen=10,notebook=20

The items included in "listBox1" are the "pen" and "notebook". If I click notebook an item will show in list box 2: 1,2 then if I click "1", text box 1.text=20 because notebook is 20*1=20

Answer 1

So, I'm just going to create an enumeration for your items.

public enum ListBoxItemThing
{
    Pen = 10, Notebook = 20
}

And then I'll add these to "listBox1" inside the form constructor.

public Form1()
{
    InitializeComponent();
    foreach(ListBoxItemThing item in Enum.GetValues(typeof(ListBoxItemThing)))
    {
        listBox1.Items.Add(item);
    }
}

And then use this procedure to do the calculation for textBox1:

private void Calculate()
{
    int a = (int)(listBox1.SelectedItem as ListBoxItemThing);
    int b = int.Parse(listBox2.SelectedItem.ToString());
    textBox1.Text = (a * b).ToString();
}