This example makes the items in a menu behave like a radio button group so when you select one, it displays a check mark and the others don't.

The key is the CheckMenuItem function.

This function takes as parameters a menu and a menu item. It loops through the objects contained in the menu. If an object is a menu item (e.g. not a separator or something else), the code sets its Checked property appropriately.

// Check this menu item and uncheck the others.
private void mnuViewOption_Click(object sender, EventArgs e)
{
    // Check the menu item.
    ToolStripMenuItem item = sender as ToolStripMenuItem;
    CheckMenuItem(mnuView, item);

    // Do something with the menu selection.
    // You could use a switch statement here.
    // This example just displays the menu item's text.
    MessageBox.Show(item.Text);
}