Работа с listBox

listBox1.SelectedIndex = 2;

public Form1()
{
    InitializeComponent();
    ListBox listBox = new ListBox
    {
        Left = 10,
        Top = 40,
        Height = 200
    };
    listBox.Items.AddRange(Enumerable.Range(0, 10).
        Select(x => "Item" + x.ToString()).ToArray());
    Button button = new Button
    {
        Left = 10,
        Top = 10,
        Text = "Start"
    };
 
    Timer timer = new Timer();
    int selectedItem = -1;
    button.Click += delegate
    {
        timer.Enabled = !timer.Enabled;
        selectedItem = -1;
        button.Text = timer.Enabled ? "Stop" : "Start";
    };
                        
    timer.Tick += delegate
    {
        selectedItem++;
        if (selectedItem == listBox.Items.Count)
            selectedItem = 0;
        listBox.SelectedIndex = selectedItem;
    };
    this.Controls.AddRange(new Control[] { button, listBox });
}