unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Label2: TLabel;
    Button1: TButton;
    Edit1: TEdit;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  const pi=3.14159;
implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var r,c,s:real;
begin
if edit1.text='' then
showmessage('输入为空，请重新输入！') //如果没有输入数据 则提示
else
begin
r:=strtofloat(edit1.text);
c:=2*pi*r;
s:=pi*sqr(r);
label2.Caption:='该圆的周长是：'+floattostr(c)+chr(13)+'面积是：'+floattostr(s); //显示结果
end;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
form1.Close;  //退出按钮的事件代码
end;

end.