try
            {
                var random = new Random();
                for (var i = 0; i < int.Parse(textBox1.Text); i++)
                {
                    listBox1.Items.Clear();
                    listBox1.Items.Add(random.Next(10, 100));
                }
            }
            catch (FormatException ex)
            {
                MessageBox.Show(ex.Message);
            }