stack.pas

《Kylix程序设计》一书中附带的例程源代码

unit Stack;

interface

uses
  SysUtils, Types, Classes;

type
  TStack = class( TObject )
  protected
    FCount: Integer;
    FItems: array of Real;
  public
    constructor Create(); overload;
    constructor Create( Size: Integer ); overload;
    procedure Clear();
    procedure Push( Item: Real );
    function Pop( var Item: Real ): Boolean;
    function Peek( var Item: Real ): Boolean;
    function IsEmpty(): Boolean;
    destructor Destroy();
  end;

implementation

{ TStack }

constructor TStack.Create;
begin
  FCount := 0;
  SetLength( FItems, 0 );
end;

procedure TStack.Clear;
begin
  if Assigned( FItems ) then
  begin
    FCount := 0;
    FItems := nil;
  end;
end;

constructor TStack.Create(Size: Integer);
begin
  FCount := 0;
  SetLength( FItems, Size );
end;

destructor TStack.Destroy;
begin
  if Assigned( FItems ) then
  begin
    FItems := nil;
  end;
end;

function TStack.IsEmpty: Boolean;
begin
  Result := ( FCount = 0 );
end;

function TStack.Peek( var Item: Real ): Boolean;
begin
  if FCount > 0 then
  begin
    Item := FItems[ FCount - 1 ];
    Result := true;
  end
  else
  begin
    Result := false;
  end;
end;

function TStack.Pop( var Item: Real ): Boolean;
begin
  if FCount > 0 then
  begin
    Item := FItems[ FCount - 1 ];
    FItems := Copy( FItems, 0, FCount - 1 );
    Dec( FCount );
    Result := true;
  end
  else
  begin
    Result := false;
  end;
end;

procedure TStack.Push(Item: Real);
begin
  if Length( FItems ) <= FCount  then
    SetLength( FItems, FCount + 1 );
  FItems[ FCount ] := Item;
  Inc( FCount );
end;

end.