WHY?


type hlist=^list;

list=record
    data: longint;
    l,r: hlist;
    end;


var n,i:longint;
    a:array[1..3000] of longint;
    head: hlist;

procedure add(var v:hlist; x:longint);
    begin
    if v=nil then
        begin
        new(v);
        v^.data:=x;
        end
    else if x>v^.data then add(v^.r, x)
                     else add(v^.l, x);
    end;

procedure draw(var v:hlist);
        begin
        if not (v=nil) then
            begin
            draw(v^.r);
            draw(v^.l);
            write(v^.data,' ');
            dispose(v);
            end;
        end;
begin
readln(n);
for i:=n downto 1 do read(a[i]);
for i:=1 to n do add(head, a[i]);
draw(head);
end.

The same error!
I don't understand why and what does mean acess violation?
Help, please!

program p1136;
  type arbore=^nod;
       nod=record
             info:word;
             left,right:arbore;
           end;
  var t,r,q:arbore;
      n,i:integer;
      a:array [1..3000] of word;
procedure postordine(t:arbore);
  begin
    if t<>nil then
      begin
        postordine(t^.right);
        postordine(t^.left);
        write(t^.info,' ');
      end;
  end;
begin
  readln(n);
  for i:=n downto 1 do read(a[i]);
  new(t);new(q);new(r);t^.info:=a[1];
  for i:=2 to n do
    begin
      r:=t;
      while q<>nil do
        begin
          if a[i]>r^.info then begin new(q);q:=r^.right;end
                          else begin new(q);q:=r^.left;end;
          if q<>nil then r:=q;
        end;
      new(q);q^.info:=a[i];
      if r^.info<a[i] then r^.right:=q else r^.left:=q;
    end;
  postordine(t);
end.