string stringbuilder

参考 https://www.cnblogs.com/kakakade/p/4562467.html  

https://www.cnblogs.com/tonysuen/archive/2010/03/04/1678447.html

 Length  IndexOf   Substring()  split join  Equals  CompareTo EndsWith   Insert  Remove Replace  PadLeft PadRight Concat ToUpper  ToLower  Trim TrimEnd 

StringBuilder

EnsureCapacity  Append AppendFormat  Insert Remove Replace