title: How to close previous mdi child in parent form
body: <p>I have a mdi parent <code>form</code> and I open my other <code>forms</code> in run time as mdi child form by this code:</p>
  
  <pre><code>private void MenuItem_Click(object sender, EventArgs e)
  {
      childform = new childform ();
      frm.MdiParent = Mdiparent;
      frm.WindowState = FormWindowState.Maximized;
      frm.Show();
  }
  </code></pre>
  
  <p>but the problem is: When current form is open, user can open another form and it can be repeated several times so that each form is opened
  what's code for closing the current child form <strong>before</strong> user open a new child form??</p>