没有注释的代码就是一坨屎，又烂又臭。
在写代码时就应该添加注释，这时在你的脑子里的是清晰完整的思路。
如果在代码最后再添加注释，它将花费你双倍的时间。
1、对每个类添加注释：包括摘要信息，作者信息，最近修改日期等；
// AppReviewAlertView.h
// iSuzhouCity
//
// Created by Chen Nan on 5/24/11.
// Copyright 2011 Yulong. All rights reserved.
//
// Utility classes
// Prompts users to rate the app via App Store,
// if they have use the app for defined days and defined times.
//
// Revision History
// 2011-05-24 | Charles | First draft.
// 2011-06-29 | Charles | 设置产品化的参数.
2、对每个方法添加注释：包括用途、功能和返回值。
/*
Must Call this method at the end of app delegate's
application:didFinishLaunchingWithOptions: method.
The rating alert
can also be triggered by appEnteredForeground: and userDidSignificantEvent:
(as long as you pass YES for canPromptForRating in those methods).
*/
+ (void)appLaunched:(BOOL)canPromptForRating;
3、对一些变量添加注释；
4、用TODO标签表示该段代码还未完成；
// TODO: implement the datepickview