PLS-00302: component 'A' must be declared

[PAVB]

In your scenario v_dup1 is a table, you need an index to handle it.

Try this...

SQL> 
SQL> declare
  2  type typ_dup1 is table of dup1%rowtype;
  3  v_dup1 typ_dup1;
  4  begin
  5  select a bulk collect into v_dup1 from dup1;
  6  for i in v_dup1.first .. v_dup1.last loop
  7  dbms_output.put_line(v_dup1(i).a);
  8  end loop;
  9  end;
 10  /

PL/SQL procedure successfully completed.

SQL>