Average value of list

Question

I want to make code that will on the first click start rotorSpeed stopwatch then on the second click add rotorSpeed.ElapsedMilliseconds to list . On the second click resets stopwatch and starts timing again, then on the third click again adds rotorSpeed.ElapsedMilliseconds to list . There are no errors in the code, but when I debug it, I get an error on double average = list.Average();

Stopwatch rotorSpeed = new Stopwatch(); List<double> list = new List<double>();

private void button1_Click(object sender, EventArgs e)
{
    i++;
    //Getting rotor speed
    if (i != 2)
    {               
        if (rotorSpeed.IsRunning)
        {
            rotorSpeed.Stop();
            list.Add(rotorSpeed.ElapsedMilliseconds);
            rotorSpeed.Start();                   
        }
        else
        {
            rotorSpeed.Reset();
            rotorSpeed.Start();
        }
    }

    double average = list.Average();
    textBox2.Text = average.ToString();
}

This is the error I get:

An unhandled exception of type 'System.InvalidOperationException' occurred in >System.Core.dll

Additional information: Sequence contains no elements

Answer 1

Your list is empty and so calling Average() on it throwing exception. Change the below line

double average = list.Average();

to

double average = list.Count > 0 ? list.Average() : 0.0;

Answer 2

if (list.Count > 0)
{
    textBox2.Text = list.Average().ToString();
}

Answer 3

if (list.Count > 1)
{
    double average = list.Average();
    textBox2.Text = average.ToString();
    rotorSpeed.Stop();
}

This works just fine. Thanks!