private void button2_Click(object sender, EventArgs e)
        {
            available_rooms a = new available_rooms();

            this.Visible = false;
            a.Visible    = true;
        }
 private void studentBillToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (avroom == null)
     {
         avroom             = new available_rooms();
         avroom.MdiParent   = this;
         avroom.FormClosed += avroom_FormClosed;
         avroom.Show();
     }
     else
     {
         avroom.Activate();
     }
 }
 void avroom_FormClosed(object sender, FormClosedEventArgs e)
 {
     avroom = null;
 }