unit Unit1;

interface

uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;

type

  TForm1 = class(TForm)

    btn1: TButton;

    btn2: TButton;

    edt2: TEdit;

    lbl1: TLabel;

    dlgOpen1: TOpenDialog;

    procedure btn1Click(Sender: TObject);

    procedure btn2Click(Sender: TObject);

  private

    { Private declarations }

  public

    { Public declarations }

  end;

var

  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.btn1Click(Sender: TObject);

var

  i:Integer;

  sFile:string;

  ms:TMemoryStream;

  buf:string;

begin

  ms:= TMemoryStream.Create;

  try

  if dlgOpen1.Execute then

  begin

    sfile:= dlgOpen1.FileName;

    ms.LoadFromFile(sFile);

    //ms.Position:=ms.Size;

    buf:= edt2.Text;

    ms.Seek(,soFromBeginning);

    ms.WriteBuffer(buf,SizeOf(buf));

    ms.SaveToFile(ChangeFileExt(sFile,'.a'));

  end;

  finally

    ms.Free;

  end;

end;

procedure TForm1.btn2Click(Sender: TObject);

var

  i:Integer;

  sFile:string;

  ms1,ms2:TMemoryStream;

  buf:string;

begin

  ms1:= TMemoryStream.Create;

  ms2:= TMemoryStream.Create;

  try

    if dlgOpen1.Execute then

    begin

      sfile:= dlgOpen1.FileName;

      ms1.LoadFromFile(sFile);

      ms1.Seek(SizeOf(edt2.Text),soFromBeginning);

      ms1.WriteBuffer(buf,SizeOf(buf));

      ms2.Position:=;

      ms2.ReadBuffer(buf,SizeOf(buf));

      ms2.SaveToFile(ChangeFileExt(sFile,'.b'));

    end;

  finally

    ms1.Free;

    ms2.Free;

  end;

end;

end.