private void button3_Click(object sender, EventArgs e)
        {
            foreach (Form f in this.MdiChildren)
            {
                if (f.GetType() == typeof(CHECKED_OUT))
                {
                    f.Activate();
                    return;
                }
            }
            Form ot_cat = new CHECKED_OUT();

            ot_cat.MdiParent = this;
            ot_cat.Show();
        }
        private void cHECKOUTToolStripMenuItem_Click(object sender, EventArgs e)
        {
            foreach (Form f in this.MdiChildren)
            {
                if (f.GetType() == typeof(CHECKED_OUT))
                {
                    f.Activate();
                    return;
                }
            }
            Form room = new CHECKED_OUT();

            room.MdiParent = this;
            room.Show();
        }