how to get minimum item in a block- oracle form? what's wrong?

[kaforms]

declare 
    v_purchase number; 
begin
         SELECT min(software.purchase_cost)
           into v_purchase
      from hardware, software
      where :hardware.hw_serial_num = software.hw_serial_num;
 
      go_block('software');
      first_record;
 
      for i in 1..:system.last_record 
       loop
              go_record(i);
       if nvl(:software.purchase_cost,0) = v_purchase then
 
      exit;
        else 
        next_record;
            end if;     
      end loop;
 
 end;