Code:

unit Unit1;

interface

uses

SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,

StdCtrls, ExtCtrls, Forms;

type

TForm1 = class(TForm)

   Memo1: TMemo;

   procedure FormCreate(Sender: TObject);

   procedure Memo1KeyPress(Sender: TObject; var Key: Char);

public

   MaxCharsPerLine, MaxLines: Integer;

   function MemoLine: Integer;

   function LineLen(r: Integer): Integer;

   function NRows: Integer;

end;

var

Form1: TForm1;

implementation

{$R *.DFM}

function TForm1.NRows: Integer;

begin

with Memo1 do

   Result := 1 + SendMessage(Handle, EM_LINEFROMCHAR, GetTextLen - 1, 0);

end;

function TForm1.LineLen(r: Integer): Integer;

var

r1, r2: Integer;

begin

with Memo1 do

begin

   r1 := SendMessage(Handle, EM_LINEINDEX, r, 0);

   if (r > NRows - 1) then

     r2 := SendMessage(Handle, EM_LINEINDEX, r + 1, 0) - 2 {-CR/LF}

   else

     r2 := GetTextLen;

end;

Result := r2 - r1;

end;

function TForm1.MemoLine: Integer;

begin

with Memo1 do

   Result := SendMessage(Handle, EM_LINEFROMCHAR, SelStart, 0);

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

MaxCharsPerLine := 8;

MaxLines := 4;

end;

procedure TForm1.Memo1KeyPress(Sender: TObject; var Key: Char);

begin

with Memo1 do

begin

   case Key of

     ' '..#255: if (LineLen(MemoLine) >= MaxCharsPerLine) then

         Key := #0;

     #10, #13: if (NRows >= MaxLines) then

         Key := #0;

     #8: if (SelStart = SendMessage(Handle, EM_LINEINDEX, MemoLine, 0)) then

         Key := #0;

   end;

end;

end;

end.

Code:

procedure TForm1.Memo1Change(Sender: TObject);

const

  MaxLineCount = 5;

begin

  if Memo1.Lines.Count > MaxLineCount then

    // undo the last change

   // letze Дnderung rьckgдngig machen

   Memo1.Perform(EM_UNDO, 0, 0);

  // The EM_EMPTYUNDOBUFFER message clears the undo flag,

// which means that you can no longer undo your last change

// to the edit control.

// Die Message EM_EMPTYUNDOBUFFER lцscht das UnDo Flag,

// damit kann die letzte Дnderung nicht Rьckgдngig gemacht werden.

Memo1.Perform(EM_EMPTYUNDOBUFFER, 0, 0);

end;