unit MainUnit;

interface

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

type
  PRing = ^TRing;
  TRing = record
     Element: Integer;
     PNextEl: PRing;
  end;
  TMainForm = class(TForm)
    btCreate: TButton;
    btAdd: TButton;
    btDelete: TButton;
    MainMenu: TMainMenu;
    Help: TMenuItem;
    About: TMenuItem;
    PopupMenu: TPopupMenu;
    procedure btCreateClick(Sender: TObject);
    procedure btAddClick(Sender: TObject);
    procedure btDeleteClick(Sender: TObject);
    procedure HelpClick(Sender: TObject);
    procedure AboutClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  MainForm: TMainForm;
  Head, CurEL: PRing;


implementation

{$R *.dfm}

uses AddUnit, DeleteUnit;

procedure TMainForm.AboutClick(Sender: TObject);
begin
   ShowMessage('Zhenya Yakubovich 851001');
end;

procedure TMainForm.btAddClick(Sender: TObject);
begin
   AddForm.ShowModal;
end;

procedure TMainForm.btCreateClick(Sender: TObject);
begin
   Head := nil;
   CurEl := nil;
   btAdd.Enabled := True;
   btDelete.Enabled := False;
end;

procedure TMainForm.btDeleteClick(Sender: TObject);
begin
   DeleteForm.ShowModal;
end;

procedure TMainForm.HelpClick(Sender: TObject);
begin
   ShowMessage('This program implements work with ring data structure.' + #13#10 +
     ' Available features: create a new ring, add, delete, view elements.');
end;

end.

unit AddUnit;

interface

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

type
  TAddForm = class(TForm)
    AddGrid: TStringGrid;
    Count: TEdit;
    lbCount: TLabel;
    btAddEl: TButton;
    procedure FormActivate(Sender: TObject);
    procedure CountChange(Sender: TObject);
    procedure AddGridKeyPress(Sender: TObject; var Key: Char);
    procedure AddGridSetEditText(Sender: TObject; ACol, ARow: Integer;
      const Value: string);
    procedure btAddElClick(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  AddForm: TAddForm;
  procedure AddElement(var CurEl: PRing; Head: PRing; Element: Integer);
  external 'AddElem.dll' name 'AddElement';

implementation

{$R *.dfm}

procedure TAddForm.AddGridKeyPress(Sender: TObject; var Key: Char);
const
   ValidSymbols = ['0'..'9', '-'];
var
   i: Integer;
begin
   if not((Key in ValidSymbols) or (Key = #8)) then
      Key := #0;
   with Sender as TStringGrid do
   begin
      if (Key in ValidSymbols) and (Length(Cells[Col, Row]) > 7) then
      begin
         Key := #0;
         ShowMessage('Maximum length of symbols: 8.');
      end;
      if (Key = '0') and (Pos('0', Cells[Col, Row]) = 1) and (Length(Cells[Col, Row]) = 1) then
         Key := #0;
      if (Key = '-') and (Length(Cells[Col, Row]) >= 1) then
         Key := #0;
      if (Key = '0') and (Pos('-', Cells[Col, Row]) = 1) and
        (Length(Cells[Col, Row]) = 1) then
         Key := #0;
   end;
end;

procedure TAddForm.AddGridSetEditText(Sender: TObject; ACol, ARow: Integer;
  const Value: string);
var
   i: Byte;
   IsFull: Boolean;
begin
   IsFull := True;
   with Sender as TStringGrid do
   begin
      for i := 0 to RowCount - 1 do
         if Length(Cells[1, i]) = 0 then
            IsFull := False;
      if IsFull then
         btAddEl.Enabled := True
      else
         btAddEl.Enabled := False;
   end;
end;

procedure TAddForm.btAddElClick(Sender: TObject);
var
   i: Byte;
begin
   i := 0;
   if Head = nil then
   begin
      New(Head);
      CurEl := Head;
      CurEl^.PNextEl := Head;
      CurEl^.Element := StrToInt(AddGrid.Cells[1, 0]);
      i := 1;
   end;
   while i < AddGrid.RowCount do
   begin
      {CurEl^.PNextEl := nil;
      New(CurEl^.PNextEl);
      CurEl := CurEl^.PNextEl;
      CurEl^.Element := StrToInt(AddGrid.Cells[1, i]);
      CurEl^.PNextEl := Head;}
      AddElement(CurEl, Head, StrToInt(AddGrid.Cells[1, i]));
      Inc(i);
   end;
   MainForm.btDelete.Enabled := True;
   AddForm.Close;
end;

procedure TAddForm.CountChange(Sender: TObject);
var
   i: Byte;
begin
   with Sender as TEdit do
   begin
      if Length(Text) = 0 then
      begin
         with AddGrid do
         begin
            Cols[0].Clear;
            Cols[1].Clear;
            Cells[0, 0] := '1';
            RowCount := 1;
            ScrollBars := ssNone;
            Width := 102;
            Options := Options - [goEditing];
         end;
         btAddEl.Enabled := False;
      end
      else
      with AddGrid do
      begin
         Options := Options + [goEditing];
         AddGrid.RowCount := StrToInt(Text);
         if AddGrid.RowCount > 3 then
         begin
            AddGrid.ScrollBars := ssVertical;
            AddGrid.Width := 124;
         end;
         for i := 1 to StrToInt(Text) - 1 do
            AddGrid.Cells[0, i] := IntToStr(i + 1);
      end;
   end;
end;

procedure TAddForm.FormActivate(Sender: TObject);
begin
   AddGrid.ColWidths[0] := 20;
   AddGrid.Width := 102;
   AddGrid.Cells[0, 0] := '1';
end;

procedure TAddForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
   with AddGrid do
   begin
      Cols[0].Clear;
      Cols[1].Clear;
      Cells[0, 0] := '1';
      RowCount := 1;
      ScrollBars := ssNone;
      Width := 102;
   end;
   Count.Text := '';
   btAddEl.Enabled := False;
end;

end.

library AddElem;

uses
  System.SysUtils,
  System.Classes;

{$R *.res}

type
   PRing = ^TRing;
   TRing = record
     Element: Integer;
     PNextEl: PRing;
   end;

procedure AddElement(var CurEl: PRing; Head: PRing; Element: Integer);
begin
   CurEl^.PNextEl := nil;
   New(CurEl^.PNextEl);
   CurEl := CurEl^.PNextEl;
   CurEl^.Element := Element;
   CurEl^.PNextEl := Head;
end;

exports AddElement;

begin
end.

unit DeleteUnit;

interface

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

type
  TDeleteForm = class(TForm)
    Count: TEdit;
    lbCount: TLabel;
    DelGrid: TStringGrid;
    btDelEl: TButton;
    procedure CountChange(Sender: TObject);
    procedure btDelElClick(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  DeleteForm: TDeleteForm;

implementation

uses MainUnit;

{$R *.dfm}

procedure TDeleteForm.btDelElClick(Sender: TObject);
var
   i: Byte;
   DelEl, Temp, OldHead: PRing;
begin
   i := 0;
   OldHead := Head;
   CurEl := Head;
   while (CurEl^.PNextEl <> OldHead) and (i < StrToInt(Count.Text)) do
   begin
      Dispose(Head);
      Head := CurEl^.PNextEl;
      CurEl := Head;
      Inc(i);
   end;
   if (CurEl^.PNextEl = OldHead) and (i < StrToInt(Count.Text)) then
   begin
      Head := nil;
      CurEl := nil;
      ShowMessage('Ring is empty.');
      DelGrid.Visible := False;
      Count.Text := '';
      MainForm.btDelete.Enabled := False;
      DeleteForm.Close;
   end
   else
   begin
      while (CurEl^.PNextEl <> OldHead) do
         CurEl := CurEl^.PNextEl;
      CurEl^.PNextEl := Head;
      CurEl := Head;
      DelGrid.Visible := True;
      Count.Text := '';
      btDelEl.Enabled := False;
      i := 0;
      DelGrid.ColWidths[0] := 20;
      DelGrid.Width := 102;
      DelGrid.ScrollBars := ssNone;
      while CurEl^.PNextEl <> Head do
      begin
         DelGrid.RowCount := i + 1;
         DelGrid.Cells[0, i] := IntToStr(i + 1);
         DelGrid.Cells[1, i] := IntToStr(CurEl^.Element);
         CurEl := CurEl^.PNextEl;
         Inc(i);
      end;
      DelGrid.RowCount := i + 1;
      DelGrid.Cells[0, i] := IntToStr(i + 1);
      DelGrid.Cells[1, i] := IntToStr(CurEl^.Element);
      if i > 3 then
      begin
         DelGrid.Width := 124;
         DelGrid.ScrollBars := ssVertical;
      end;
   end;
end;

procedure TDeleteForm.CountChange(Sender: TObject);
begin
   if Length(Count.Text) = 0 then
      btDelEl.Enabled := False
   else
      btDelEl.Enabled := True;
end;

procedure TDeleteForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
   with DelGrid do
   begin
      Cols[0].Clear;
      Cols[1].Clear;
      RowCount := 1;
      ScrollBars := ssNone;
      Width := 102;
      Visible := False;
   end;
   Count.Text := '';
end;

end.