Console.WriteLine($"int? is {(IsNullable(typeof(int?)) ? "nullable" : "non nullable")} type");
Console.WriteLine($"int is {(IsNullable(typeof(int)) ? "nullable" : "non nullable")} type");

bool IsNullable(Type type) => Nullable.GetUnderlyingType(type) != null;

// Output:
// int? is nullable type
// int is non nullable type