internal class Program
{
    private static void Main(string[] args)
    {
        MyClass cls = new();
        cls.NullableTest();
    }

}

class MyClass
{
    double _Sum = 0;
    DateTime _Time;
    bool? _Selected;

    public void CheckInput(int? i, double? d, DateTime? time, bool? selected)
    {
        if (i.HasValue && d.HasValue)
            this._Sum = (double)i.Value + (double)d.Value;

        // time값이 있는 체크.
        if (!time.HasValue)
            throw new ArgumentException();
        else
            this._Time = time.Value;

        // 만약 selected가 NULL이면 false를 할당
        this._Selected = selected ?? false;
    }
    public void NullableTest()
    {
        int? a = null;
        int? b = 0;
        int result = Nullable.Compare<int>(a, b);
        Console.WriteLine(result); //결과 -1

        double? c = 0.01;
        double? d = 0.0100;
        bool result2 = Nullable.Equals<double>(c, d);
        Console.WriteLine(result2); //결과 true
    }
}