不用字符串来实现 InternetURL 类-define InternetURL class to save a URL string like as　www.bit.edu.cn ，and realize the demands as follows:



0. You CAN NOT use string in the program



1. You must use MyString you just defined in the exercise3.txt to save URL string；



2. Get domain name　URL. For example, we can get　www.bit.edu.cn　　www.bit.edu.cn/jwc/080329.html ；



3. Get top domain name　URL. For example, we can get　.cn　　　www.bit.edu.cn/jwc/080329.html ；