In c# 2.0 we are given with provision of storing null values in value types also which was not possible in earlier version
In earlier version null values can be stored only in reference types but now in value types also null values can stored which requires type to be declared suffexing with ?
Nullable value types(2.0)
string s=null; //valid
int x=null; // invalid
int?x=null;//valid
This feature provides important interaction with Sql database