Delphi 中的 IfThen 函数 - 回复 "深挖洞、广积粮" 的问题

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

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

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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.