for循环介绍
http://blog.csdn.net/whackw/article/details/51789738
基本教程
http://www.jb51.net/article/49627.htm
变量定义
http://buralin.iteye.com/blog/1266310
变量延时
http://blog.csdn.net/subkiller/article/details/7344509
http://www.jb51.net/article/29323.htm?timer=tc