private void button1_Click(object sender, EventArgs e)
        {
            int      penNumber, penCap, petNumber, clinicNumber;
            string   petComments;
            DateTime DateIN, DateOUT;

            penNumber    = Convert.ToInt32(cmbPenNumber.SelectedValue.ToString());
            penCap       = 4;
            petNumber    = Convert.ToInt32(txtPNum.Text);
            petComments  = rtbComments.Text;
            DateIN       = dateTimePicker1.Value;
            DateOUT      = dateTimePicker2.Value;
            clinicNumber = Convert.ToInt32(cmbClinicNumber.SelectedValue.ToString());

            database.BookPen(penNumber, penCap, penStatus, petNumber, petComments, DateIN, DateOUT, clinicNumber);

            this.Close();
        }