Null ,"

In C #, there is a null type, Int? A = NULL; it indicates that int type A can be null;
Of course, null is only associated with "" in the string type.
The difference between "" and null is that
1. "" can only be used in the string type. In addition to the string type, null can also be of another type.
2. For string S1 = "", the system will allocate space for S1, and S2 = NULL will not (as mentioned in C # advanced programming version 4th)
3. it is also in the string, during comparison and judgment; for a string S2 = NULL, if (s2.tostring () = NULL) cannot be used for determination; for string S1 = "", the s1.tostring () method can be used. However, if (s1.tostring () = NULL) is used to determine whether it is syntactically correct, logically incorrect S1, if (s1.tostring () = "") is true;
4. For string S1 = "", "" is still used to determine the case after packing, rather than null.