trigger after with cursor

Hi..

I try trigger after insert used cursor without rowtype or cursor with
rowtype, etc:

create or replace function fn_tr_ai_pdcblc() returns trigger as '
declare
c_pdcblc cursor for select * from t_pdcblc where fc_branch=new.fc_branch
and fc_bankacct=new.fc_bankacct;
row_pdcblc t_pdcblc%rowtype;
balance decimal(30,5);
begin
balance:=0;
open c_pdcblc;
for c_pdc in 1..(select count(*) from t_pdcblc where
fc_branch=new.fc_branch and fc_bankacct=new.fc_bankacct and
fd_trxdate>=new.fd_trxdate) loop
fetch c_pdcblc into row_pdcblc;
if (select count(*) from t_pdcblc where fc_branch=new.fc_branch and
fc_bankacct=new.fc_bankacct and fd_trxdate<new.fd_trxdate)>0 then
balance:=fm_balance from t_pdcblc where fc_branch=new.fc_branch
and fc_bankacct=new.fc_bankacct and fd_trxdate<new.fd_trxdate;
end if;
new.fm_balance := balance+row_pdcblc.fm_masuk-row_pdcblc.fm_keluar;
(update field fm_balance at table t_pdcblc)
balance := new.fm_balance;
end loop;
close c_pdcblc;
return new;
end;' language 'plpgsql';

create trigger tr_ai_pdcblc after insert on d_transaksi.t_pdcblc for each
row execute procedure fn_tr_ai_pdcblc();

result actually:
table t_pdcblc for field fm_balance occupied value null, ex:
fm_masuk fm_keluar fm_balance
1000 0

this must:
fm_masuk fm_keluar fm_balance
1000 0 1000

Please help me...

thanks
betty