ASP. NET ?? Operator

?? Indicates that when the left margin of the operator is null, the right margin value is displayed. Otherwise, the left margin value is displayed.
As shown in the replacement: Int C =   888 ;

// definition blank
int ? CC = null ;

//The following definition is null argument (because it is an actual value type, it cannot be converted to 'int ')
IntCN= Null;

//?? When the left region is empty, the right region is displayed. Otherwise, the left region is displayed.
Response. Write (convert. tostring (CC??C ));

Result: 888

Int ? CC =   6 ;
Response. Write (convert. tostring (CC ?? C ));

Result: 6