Delphi 中的 IfThen 函数

问题来源: http://www.cnblogs.com/del/archive/2008/11/14/1120015.html#1370413

StrUtils 单元和 Math 单元 分别有一个 IfThen 函数（注意参数是数字还是字符串）, 举例:

StrUtils 单元和 Math 单元 分别有一个 IfThen 函数, 举例:
unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses StrUtils, Math;

procedure TForm1.Button1Click(Sender: TObject);
var
  a: Integer;
  str: string;
begin
  a := ;
  str := StrUtils.IfThen(a > , 'aaa', 'bbb');
  ShowMessage(str); {aaa}

  a := -;
  str := StrUtils.IfThen(a > , 'aaa', 'bbb');
  ShowMessage(str); {bbb}

  a := ;
  str := StrUtils.IfThen(a > , 'aaa');
  ShowMessage(str); {aaa}

  a := -;
  str := StrUtils.IfThen(a > , 'aaa');
  ShowMessage(str); {}
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  str: string;
  num: Integer;
begin
  str := '万一';
  num := Math.IfThen(str <> '', , );
  ShowMessage(IntToStr(num)); {}

  str := '';
  num := Math.IfThen(str <> '', , );
  ShowMessage(IntToStr(num)); {}

  str := '万一';
  num := Math.IfThen(str <> '', );
  ShowMessage(IntToStr(num)); {}

  str := '';
  num := Math.IfThen(str <> '', );
  ShowMessage(IntToStr(num)); {}
end;

end.