C#

public class MyClass
{
  // Initialize a new array with a length of two (thus index 0 and 1):
  private Button[] _buttons = new Button[2];
  private int _counter = 0;
  
  // Handle the events of your buttons.
  public MyClass()
  {
    MyButton1.Click += new EventHandler(Button_Click);
    MyButton2.Click += new EventHandler(Button_Click);
    MyButton3.Click += new EventHandler(Button_Click);
    // Etc...
  }
  
  private void Button_Click(object sender, EventArgs e)
  {
    // Assign your button to the array,
    _buttons[_counter] = (Button)sender;
    // and increase the counter by 1.
    _counter++;
  }
}

if (_counter > _buttons.Length - 1) _counter = 0;

public static string ShortenString(string s, int len)
{
  if( s.Length <= len )
    return "";
  return s.Substring(0, s.Length - len);
}

...
string sNewString = MyClass.ShortenString(sOldString, 2);