var
  Form1: TForm1;
  a:integer;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
c:string;
s:string;
begin
a:=a+1;
s:='BCDEFGHIKLMNOPQRSTUVXYZ';
c:=copy(s,a,1);
if Edit1.Text='' then
Edit1.Text:='A'
else
Edit1.Text:=Edit1.Text+c;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
a:=-1;
end;

end.