unit Unit1 interface uses Winapi Windows Winapi Messages System SysUti

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm1 = class(TForm)
    ListBox1: TListBox;
    Button1: TButton;
    Memo1: TMemo;
    Label1: TLabel;
    Edit1: TEdit;
    Edit2: TEdit;
    Button2: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure refreshList;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  items:array[0..1000,0..1] of string;

implementation

{$R *.dfm}

function getLastId:integer;
var
  i:integer;
begin
  result:=-1;
  for i := 0 to 1000 do
  begin
    if ((Items[i,0] = '') AND (Items[i,1] = '')) then
    begin
      result:=i;
      break;
    end;
  end;
end;

procedure TForm1.refreshList;
var
  i:integer;
begin
  ListBox1.Clear;
  for i := 0 to 1000 do
  begin
    if ((Items[i,0] = '') OR (Items[i,1] = '')) then break;
    ListBox1.Items.Add(Items[i,0]+' ('+Items[i,1]+'р)');
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  i:integer;
  sum:integer;
begin
  Memo1.Lines.Clear;
  Memo1.Lines.Add('Товары:');
  sum:=0;
  for i := 0 to ListBox1.Items.Count-1 do
  begin
    if (ListBox1.Selected[i]) then
    begin
      Memo1.Lines.Add(ListBox1.Items[i]);
      sum:=sum+StrToInt(Items[i,1]);
    end;
  end;
  Label1.Caption:=IntToStr(sum);
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  lastId:integer;
begin
  lastId:=getLastId;
  Items[lastId,0]:=Edit1.Text;
  Items[lastId,1]:=Edit2.Text;
  refreshList;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  i:integer;
begin
  Items[0,0]:='Хрень №1'; Items[0,1]:='20';
  Items[1,0]:='Хрень №2'; Items[1,1]:='234';
  Items[2,0]:='Хрень №3'; Items[2,1]:='102';
  Items[3,0]:='Хрень №4'; Items[3,1]:='41';
  Items[4,0]:='Хрень №5'; Items[4,1]:='32';
  Items[5,0]:='Хрень №6'; Items[5,1]:='50';
  refreshList;
end;

end.