How to sum all numbers in a Listbox using TextBox?

Question

I want to count and sum all values in a ListBox. For example, I have the following values in my ListBox: 4, 6, 1, 7. My current value is 18. If I add a 2 with a TextBox, I need to get 20 and if I add 5 I need to get 25 in total.

If I try it with the below code, it gives me a whole other number.

Here is my code:

private void AddButton_Click(object sender, EventArgs e)
{
    decimal sum;
    listBox2.Items.Add(TextBox1.Text);
    TextBox1.Text = "";

    for (int i = 0; i < listBox2.Items.Count; i++)
    {
        sum += Convert.ToDecimal(listBox2.Items[i].ToString());
    }

    Label1.Text = sum.ToString();
}

Answer 1

You missed to initialize default value of sum. Assign sum = 0 before adding values to sum variable

private void AddButton_Click(object sender, EventArgs e)
{
    decimal sum = 0;  //Set sum = 0  by default
    listBox2.Items.Add(TextBox1.Text);
    TextBox1.Text = "";

    for (int i = 0; i < listBox2.Items.Count; i++)
    {
        //To check value of sum after each iteration, you can print it on console
        Console.WriteLine("Sum =" +sum);
        sum += Convert.ToDecimal(listBox2.Items[i].ToString());
    }

    Label1.Text = sum.ToString();
}