Question

Why visual studio give me an error with :

public void afunction(int? bar){ somecode }

afunction(String.IsNullOrEmpty(Request["foo"])?null:int.Parse(Request["foo"]));

it give me there no implcit conversion between null and int

Answer 1

The 2nd and 3rd operands for the ? operator must have compatible types. They don’t in your case, the 2nd is null, the 3rd is int. There is no implicit conversion from int to null nor from null to int. Only explicit ones, like a cast to object or Nullable<int>. You might consider using this:

afunction(String.IsNullOrEmpty(Request["foo"]) ? default(int?) : int.Parse(Request["foo"]));

No problem here since there is an implicit conversion from int to int?