C#

using System.ComponentModel;
...
this.Closing += new CancelEventHandler(this.ClosingEventHandler);
bool ShutDownInvoked = false;
...
public void CloseRequested_Click(object sender, EventArgs e)
{
    ShutDownInvoked = true;
    this.Close();
}
public void ClosingEventHandler(object sender, CancelEventArgs e)
{
    if (ShutDownInvoked)
       return;
    this.Hide();
    e.Cancel = true;
}

public class MyForm : Form
{
  // ...
  protected override void OnClosing(CancelEventArgs e)
  {
    e.Cancel = true;
    Hide();
  }
  // Make sure you have a menu or some other way to close the form, though.
  private void mnuFileExit_Click(object sender, EventArgs e)
  {
    // The handler for a <code>MenuItem</code> to exit the application...
    Application.Exit();
  }
}

int len = mystring.Length > 200? 200: mystring.Length;
string temp = String.Concat(mystring.SubString(0, len), "...");