Lista circulara dublu inlantuita: parcurgere

>Parcurgerea listei circulare dublu inlantuite inainte si inapoi.

program lcdi;
uses crt;
type nod=^ref;
     ref=record
           info:integer;
           prec,urm:nod;
        end;
var p,prim,ultim:nod;
    n:integer;
procedure creare_lcdi;
begin
     prim:=nil;
     ultim:=nil;
     write('Introd. info: ');readln(n);
     while n<>0 do begin
                        new(p);
                        p^.info:=n;
                        if prim=nil then begin
                                              p^.urm:=nil;
                                              p^.prec:=nil;
                                              ultim:=p;
                                              prim:=p;
                                         end
                                     else begin
                                               p^.urm:=nil;
                                               p^.prec:=ultim;
                                               ultim^.urm:=p;
                                               ultim:=p;
                                          end;
                        write('Introd. info: ');readln(n);
                    end;
end;
procedure afisare;
begin
     p:=prim;
     while p<>nil do
     begin
          write(p^.info,' ');
          p:=p^.urm;
     end;
end;
procedure parcurg_direct;
begin
     writeln('Lista circulara dublu inlantuita parcursa direct:');
     p:=prim;
     while p<>nil do
     begin
          write(p^.info,' ');
          p:=p^.urm;
     end;
     write(prim^.info);
end;
procedure parcurg_invers;
begin
     writeln('Lista circulara dublu inlantuita parcursa invers:');
     p:=ultim;
     while ultim<>nil do
     begin
          write(ultim^.info,' ');
          ultim:=ultim^.prec;
     end;
     write(p^.info);
end;
BEGIN
clrscr;
creare_lcdi;
afisare;writeln;
parcurg_direct;writeln;
parcurg_invers;
readln;
END.