string manipulation

["Gep" <nodsa@sdfsffds.net>]

Is it possible to declare a string to be exactly 10 characters long and
still be a variable? then
for example

declare V_string as being exactly 10 characters


while not valid
loop
get_line(V_string, V_length);

if v_Art_lng = t_Art_article.t_art_proprietaire.v_nas'length then
      Skip_Line;
      Valid := True;
else
    valid :=false;
    Put("invalid");
end if;

end loop;

anything not in the range of declared string (in this case being10) would be
declared as invalid...any ideas?
I dont want to to have any explicit statement of 10 like "if V_length = 10
then"    in this little procedure as it will be getting strings of various
length.