Delphi 中的 IfThen 函数

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 := 1;
  str := StrUtils.IfThen(a > 0, ‘aaa‘, ‘bbb‘);
  ShowMessage(str); {aaa}
 
  a := -1;
  str := StrUtils.IfThen(a > 0, ‘aaa‘, ‘bbb‘);
  ShowMessage(str); {bbb}
 
  a := 1;
  str := StrUtils.IfThen(a > 0, ‘aaa‘);
  ShowMessage(str); {aaa}
 
  a := -1;
  str := StrUtils.IfThen(a > 0, ‘aaa‘);
  ShowMessage(str); {}
end;
 
procedure TForm1.Button2Click(Sender: TObject);
var
  str: string;
  num: Integer;
begin
  str := ‘万一‘;
  num := Math.IfThen(str <> ‘‘, 99, 11);
  ShowMessage(IntToStr(num)); {99}
 
  str := ‘‘;
  num := Math.IfThen(str <> ‘‘, 99, 11);
  ShowMessage(IntToStr(num)); {11}
 
  str := ‘万一‘;
  num := Math.IfThen(str <> ‘‘, 99);
  ShowMessage(IntToStr(num)); {99}
 
  str := ‘‘;
  num := Math.IfThen(str <> ‘‘, 99);
  ShowMessage(IntToStr(num)); {0}
end;
 
end.