Question

private void btnStart_Click(object sender, EventArgs e)
{
    Random random = new Random();
    int randomNumber = random.Next(0, 1000);
    int RandomTolerance = 5 || 10;
    lblRandomValue.Text = randomNumber + "000" + "O" + RandomTolerance;
}

I do not understand how to allow the RandomTolerance to choose between 5 and 10 only as an integer.

Answer 1

int RandomTolerance=random.Next(0,2)<1?5:10;

As a side note, reseeding your random number generator over and over is usually a bad idea. You should read up on how random number generators work.