?? Operator (C # reference)

?? An operator is a null merge operator that defines the types that can be null values and the default values of reference types. If the left operand of this operator is not null, this operator returns the left operand; otherwise, the right operand is returned.

class NullCoalesce{    static int? GetNullableInt()    {        return null;    }    static string GetStringValue()    {        return null;    }    static void Main()    {        // ?? operator example.        int? x = null;        // y = x, unless x is null, in which case y = -1.        int y = x ?? -1;        // Assign i to return value of method, unless        // return value is null, in which case assign        // default value of int to i.        int i = GetNullableInt() ?? default(int);        string s = GetStringValue();        // ?? also works with reference types.         // Display contents of s, unless s is null,         // in which case display "Unspecified".        Console.WriteLine(s ?? "Unspecified");    }}