source: branches/topdown/Apps/AppCalc.pas

unit AppCalc;

interface

uses
  Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, OsSystem;

type
  TOperation = (opNone, opAdd, opMultiply);

  { TFormCalculator }

  TFormCalculator = class(TFormTask)
    ButtonCompute: TButton;
    ButtonAdd: TButton;
    ButtonMultiply: TButton;
    EditInput: TEdit;
    procedure ButtonAddClick(Sender: TObject);
    procedure ButtonComputeClick(Sender: TObject);
    procedure ButtonMultiplyClick(Sender: TObject);
    procedure FormClose(Sender: TObject; var CloseAction: TCloseAction);
  private

  public
    ResultValue: Integer;
    LastOp: TOperation;
    procedure Calculate;
  end;


implementation

{$R *.lfm}

{ TFormCalculator }

procedure TFormCalculator.ButtonAddClick(Sender: TObject);
begin
  Calculate;
  LastOp := opAdd;
  EditInput.SetFocus;
  EditInput.SelectAll;
end;

procedure TFormCalculator.ButtonComputeClick(Sender: TObject);
begin
  Calculate;
  EditInput.SetFocus;
  EditInput.SelectAll;
end;

procedure TFormCalculator.ButtonMultiplyClick(Sender: TObject);
begin
  Calculate;
  LastOp := opMultiply;
  EditInput.SetFocus;
  EditInput.SelectAll;
end;

procedure TFormCalculator.FormClose(Sender: TObject;
  var CloseAction: TCloseAction);
begin
  Terminate;
end;

procedure TFormCalculator.Calculate;
begin
  if LastOp = opAdd then begin
    ResultValue := ResultValue + StrToInt(EditInput.Text);
  end else
  if LastOp = opMultiply then begin
    ResultValue := ResultValue * StrToInt(EditInput.Text);
  end;
  EditInput.Text := IntToStr(ResultValue);
end;

end.