C # bool? The meaning

bool?is nullable bool .

bool? first;bool second;

In the above code, would be is while would be first null second false .

?the symbol after a type was only a shortcut to the Nullable type, was bool? equivalent to Nullable<bool> .

boolis a value of type, this means the it cannot being null , so the Nullable type basically allows your to wrap value types, and be ing able to assign to null them.

bool?Can contain three different values: true , false and null .

X y X&Y x|YTrue True True TrueTrue False False TrueTrue Null Null TrueFalse True False TrueFalse False false falsefalse null false nullnull  null truenull false false  nullnullnull null null 
 
    
Ref:https://stackoverflow.com/questions/1181491/whats-the-difference-between-bool-and-bool

C # bool? The meaning