rcursion in abap

hi experts

i have this form:

form fill_tab using l_line_num

l_data.

DATA: l_datum TYPE datum,

l_erzet TYPE erzet,

l_dat1 TYPE string,

l_dat2 TYPE string.

CASE l_line_num.

WHEN '1'.

WHEN '2'.

wa_dat_dlv-delv_num = l_data.

WHEN '3'.

CONCATENATE l_data4(4) l_data2(2) l_data(2)

INTO wa_dat_dlv-delv_date.

wa_dat_dlv-delv_time = l_data+8.

WHEN '4'.

wa_dat_dlv-paz_ord_num = l_data.

WHEN '5'.

CONCATENATE l_data4(4) l_data2(2) l_data(2)

into wa_dat_dlv-order_date.

WHEN '6'.

wa_dat_dlv-cust_num = l_data.

WHEN '7'.

wa_dat_dlv-cust_desc = l_data.

WHEN '8'.

wa_dat_dlv-line_num = l_data.

WHEN '9'.

wa_dat_dlv-matnr = l_data.

WHEN '10'.

SPLIT l_data AT ' ' INTO l_dat1 l_dat2.

wa_dat_dlv-ord_amnt = l_dat1.

wa_dat_dlv-sup_amnt = l_dat2.

WHEN '11'.

wa_dat_dlv-u_o_m = l_data.

APPEND wa_dat_dlv TO it_dat_dlv.

WHEN OTHERS.

l_line_num = l_line_num - 4.

PERFORM fill_tab USING l_line_num l_data.

ENDCASE.

endform. " fill_tab

this form is a recursive form after l_line_num is greater than 11, when it happens l_line_num is updated to

l_line_num -4 and it calls the form again. but than the case don't stop.

what's the problem?

thank you

amit