说明：  1、 实现串赋值、串比较、求串长、串联接以及求子串这5种基本操作。 2、 能利用上述实现的基本操作完成置换Replace (&S, T, V)以及从串中删除一段子串StrDelete(&S,pos,len)的操作。
(1, realize assignment string, string comparison, and string a long string of serial access, as well as Child-giving this five kinds of basic operation. 2, able to realize the basic use of the above-mentioned operation is complete replacement Replace ()