[][enk]

Код:

unit Uclss;

interface

uses Dialogs;

type
  TClass = class
  Fstr: String;

  end;

implementation

end.

Код:

unit prjct;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    pB: TButton;
    procedure pBClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  MainForm: TForm1;

implementation

{$R *.dfm}
uses
  Uclss;
var
  Cls: TClass;

procedure TForm1.pBClick(Sender: TObject);
begin
  Cls.Fstr := 'WTF';
end;

end.

Как правильно обращаться к полям?Не ругайте только сильно
Пpoeкт prject.exe вызвaл иcключeниe клacca EAccessViolation c cooбщeниeм 'Access violation at address ... при нажатии на кнопку pB