Операции со строками, переход на предыдущую строку

var
  i,index:integer;
  f:textfile;
  s:string;
procedure TForm1.Next1Click(Sender: TObject);
begin
 readln(f,s);
 memo1.Lines.add(s);
 inc(i);
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
 assignfile(f,'1.txt');
 reset(f);
 I:=0;
end;
 
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
 closefile(f);
end;
 
procedure TForm1.Pred2Click(Sender: TObject);
begin
 assignfile(f,'1.txt');
 reset(f);
 index:=0;
 while index<i-1 do
 begin
  readln(f,s);
  inc(index);
 end;
 i:=i-1;
 memo1.Lines.Add(s);
end;
end.

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Unit2;
 
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
  F: TextFile;
 
implementation
 
{$R *.dfm}
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  OpenFileA(F, '1.txt');
end;
 
procedure TForm1.Button3Click(Sender: TObject);
begin
  Edit1.Text:=GetNextA(F);
end;
 
procedure TForm1.Button4Click(Sender: TObject);
begin
  ShowMessage(IntToStr(GetNextStrLenA(F)));
end;
 
procedure TForm1.Button2Click(Sender: TObject);
begin
 
end;
 
end.

unit Unit2;
 
interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
procedure OpenFileA(var F: TextFile; Path: string);
function GetNextStrLenA(var F: TextFile): integer;
function GetNextA(var F: textFile): string;
 
implementation
 
procedure OpenFileA(var F: TextFile; Path: string);
begin
  AssignFile(F, Path);
  Reset(F);
end;
 
function GetNextStrLenA(var F: TextFile): integer;
var
  L: string;
begin
  ReadLn(F, L);
  Result := Length(L);
end;
 
function GetNextA(var F: textFile): string;
var
 L: string;
begin
  ReadLn(F, L);
  Result := L;
end;
 
function GetPrevA(var F: textfile): string;
var
L: string;
N: LongInt;
begin
 N := FilePos(F);
 Seek(F, N-1);
 ReadLn(F, L);
 Result := L;
end;
 
end.