Lista circulara simplu inlantuita: creare, parcurgere, stergere

>Operatii lista circulara simplu inlantuita: creare, parcurgere, stergere.

{operatii lista circulara simplu inlantuita: creare, parcurgere, stergere}
program oplcsi;
uses crt;
type nod=^ref;
              ref=record
                        info:integer;
                        urm:nod;
              end;
var p,q,prim,ultim:nod;
    a,n:integer;
    ch:char;
procedure creare_lc;
begin
     write('  Introdu informatia nodului : ' );
     readln(n);
     prim:=nil;
     ultim:=nil;
     while n<>0 do
                begin
                     new(p);
                     p^.info:=n;
                     if prim=nil then
                                     begin
                                          prim:=p;
                                          ultim:=p;
                                          p^.urm:=nil;
                                     end
                                 else
                                     begin
                                          p^.urm:=nil;
                                          ultim^.urm:=p;
                                          ultim:=p;
                                     end;
                write('  Introdu informatia nodului : ' );
                readln(n);
       end;
end;
procedure parcurgere;
begin
     p:=prim;
     while p<>nil do
           begin
                write(p^.info,'   ');
                p:=p^.urm;
           end;
     write(prim^.info);
end;
procedure stergere;
begin
     writeln;
     write('  Valoarea de sters : ');
     readln(a);
     p:=prim;
     if p^.info=a then
                      begin
                           p:=prim^.urm;
                           dispose(prim);
                           prim:=p;
                      end
                  else
                      begin
                           while p^.urm^.info<>a do p:=p^.urm;
                           q:=p^.urm;
                           p^.urm:=q^.urm;
                           dispose(q);
                      end;
     writeln('  Noua lista este : ');
end;
BEGIN
     clrscr;
     creare_lc;writeln;
     writeln('  Lista circulara este : ');
     parcurgere;
     repeat
          stergere;
          parcurgere;writeln;
          writeln('  Mai stergi ?');
          readln(ch);
     until (ch='n') or (ch='N');
END.