Question

How could i add (DateTime?) and (long?) in C#, where long is hrs.
Result expected in DateTime

Answer 1

        DateTime dt = DateTime.Now;
        long hours = 44;
        var dt2=dt.AddHours(hours);  // uses an implicit cast from long to double
                                     // use "(double)hours" for an explicit cast

** Nullable Version **

        DateTime? dt = DateTime.Now;
        long? hours = 44;
        if(hours==null) hours=0;
        DateTime? dt2 = (dt == null) ? null : (DateTime?) ((DateTime) dt).AddHours(hours);

** Nullable Version (compact) **

        DateTime? dt = DateTime.Now;
        long? hours = 44;
        DateTime? dt2 = (dt == null) ? null : (DateTime?) dt.Value.AddHours(hours??0);

** Nullable with if statement **

        DateTime? dt = DateTime.Now;
        long? hours = 44;
        if(hours==null) hours=0;
        DateTime? dt2 = null;
        if (dt == null) 
            dt2 = (DateTime?) ((DateTime) dt).AddHours(hours);
        else 
            dt2 = null;

---

Follow up:

In the other answers, I liked the use of .Value (which looks a little cleaner than a cast), but this doesn’t remove the need to check for null in the hours parameter. btw: I tried one of the other .Value answers and got Argument 1: cannot convert from ‘long?’ to ‘double’ — i.e. you can’t forget the null check.