duas somas usando e convertendo delphi string para Double

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants,
  System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
   i:Integer;
   n:Double;
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
resultado:Double;
begin
 i:= 100;
 n := 10.50;
 resultado := i+n;
 ShowMessage(FloatToStr(resultado));
//FloatToStr de string para Double
end;

end.