提一个语言问题：(39 and 63) = 39 ？？？(50分)

procedure TForm1.Button2Click(Sender: TObject);
begin
  if (1 and 2) = 0 then //true
    showmessage('yes0');

  if (39 and 63) = 39 then //true
    showmessage('yes39');

  if (1 and 2) = 1 then //false
    showmessage('yes1');
end;

The following example uses an edit control, a button, a string grid, and seven check boxes. The check boxes correspond to the seven possible file attributes. When the button is clicked, the path specified in the edit control is searched for files matching the checked file attributes. The names and sizes of the matching files are inserted into the string grid.

procedure TForm1.Button1Click(Sender: TObject);

var
  sr: TSearchRec;
  FileAttrs: Integer;
begin
  StringGrid1.RowCount := 1;
  if CheckBox1.Checked then
    FileAttrs := faReadOnly
  else
    FileAttrs := 0;
  if CheckBox2.Checked then
    FileAttrs := FileAttrs + faHidden;
  if CheckBox3.Checked then
    FileAttrs := FileAttrs + faSysFile;
  if CheckBox4.Checked then
    FileAttrs := FileAttrs + faVolumeID;
  if CheckBox5.Checked then

    FileAttrs := FileAttrs + faDirectory;
  if CheckBox6.Checked then
    FileAttrs := FileAttrs + faArchive;
  if CheckBox7.Checked then

    FileAttrs := FileAttrs + faAnyFile;

  with StringGrid1 do
  begin
    RowCount := 0;

    if FindFirst(Edit1.Text, FileAttrs, sr) = 0 then

    begin
      repeat
        if (sr.Attr and FileAttrs) = sr.Attr then //[b]就是这句，它的作用是什么呢？为什么要这样做？谢谢！[/b]
        begin
        RowCount := RowCount + 1;
        Cells[1,RowCount-1] := sr.Name;
        Cells[2,RowCount-1] := IntToStr(sr.Size);
        end;
      until FindNext(sr) <> 0;
      FindClose(sr);
    end;
  end;
end;