Не понимаю почему выдает ошибку

procedure TForm1.Button1Click(Sender: TObject);
var f : textfile;
    i : integer;
begin
  if OpenDialog1.Execute then begin
    assignfile(f, opendialog1.FileName);
    reset(f);
    read(f, a);
    read(f, b);
    read(f, c);
    solve();
     for i := 1 to 4 do
    StringGrid1.cells[0, i - 1] := floattostr(ar[i]);
    closefile(f);
  end;
end;
 
procedure TForm1.Button2Click(Sender: TObject);
var f : textfile;
begin
  if opendialog1.Execute then begin
    assignfile(f, opendialog1.FileName);
    rewrite(f);
    write(f, ar[1] : 6 : 4, ' ', ar[2]  : 6 : 4, ' ', ar[3]  : 6 : 4, ' ',  ar[4]  : 6 : 4);
    closefile(f);
  end;
end;
 
procedure TForm1.Button3Click(Sender: TObject);
var f : file of extended;
begin
  if opendialog1.Execute then begin
    assignfile(f, opendialog1.FileName);
    rewrite(f);
    write(f, ar[1], ar[2], ar[3], ar[4]);
    closefile(f);
  end;
end;
 
procedure TForm1.Button4Click(Sender: TObject);
var f : file of extended;
    i : integer;
    t : extended;
begin
  if opendialog1.Execute then begin
    assignfile(f, opendialog1.FileName);
    reset(f);
    for i := 1 to 4 do begin
      read(f, t);
      stringgrid1.Cells[0, i - 1] := floattostr(t);
    end;
    closefile(f);
  end;
end;

if OpenDialog1.Execute then begin