关于数据类型的疑问？

unit test10;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ExtCtrls;
type
  TForm1 = class(TForm)
    Label1: TLabel;
    Shape1: TShape;
    Shape2: TShape;
    Shape3: TShape;
    Shape4: TShape;
    Shape5: TShape;
    Shape6: TShape;
    Shape7: TShape;
    Shape8: TShape;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
   private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
{$R *.DFM}
var
i:integer ;
b:string;
c:tcomponent;
procedure TForm1.FormCreate(Sender: TObject);
begin
   b:='shape';
   i:=0;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
 i:=i+1;
 label1.Caption := b + inttostr(i);
 c := Components[i];
 tComponent(Components[i]).visible := true;
end;
end.出错信息如下：[Error] test10.pas(43): Undeclared identifier: 'visible'请问我如何用表量替代控件名称？
谢谢！