Executing dynamic queries (EXECUTE)

Hello!

I need to execute a dynamic query and capture your result in a integer variable.

I´m using the statement "EXECUTE string", but I don´t obtain to capture the result of dynamic query.

See the example:

======================================================
create or replace function f_population_check() returns bigint as
'
declare
v_tot bigint;
v_query varchar(4000);
v_count integer;
r record;
begin
v_tot:= 0;
for r in select * from pg_tables loop
v_count:= 0;
v_query := ''select count(*) from '' || r.tablename;
v_count:= EXECUTE v_query;
if v_count = 0 then
RAISE NOTICE ''Empty table % '',r.tablename;
end if;
v_tot:= v_tot + 1;
end loop;
return v_tot;
end;
'
language 'plpgsql';

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ERROR: parse error at or near "$1" at character 18
CONTEXT: PL/pgSQL function "f_population_check" line 11 at assignment

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Somebody could help me?
Thanks, Carla Mello.