procedure TForm1.stlistClick(Sender: TObject);
var
stringlist:tstringlist;
begin
stringlist:= TStringList.Create;
if not FileExists ('a.txt') then
stringlist.SaveToFile('a.txt');
stringlist.loadfromfile('a.txt');
stringlist.add(st.text) ;
stringlist.savetofile('a.txt');
stringlist.Free;
end;