C#中可以用来提醒自己任务的三个符号，不过hack这个符号老是会忘，现在只好记在这里了。
//todo:将要做的工作
//hack:
//undone:未完成的工作
而且对//hack: 的用法还不是很理解。
Items labeled TODO, HACK, and UNDONE in the Task List window indicate code problems that do not keep the project from compiling, but that do cause run-time errors. You should correct these errors before running the project.