C# Cannot implicitly convert type ‘int?’ to ‘int’

c++int

I have this query:

int cid =  (from c in dc.Cs
                where c.id == cid
                select c.clientid).FirstOrDefault();

return cid;

where c.clientid is nullable. But I receive this error:

Cannot implicitly convert type 'int?' to 'int'. An explicit conversion exists (are you missing a cast?)

Best Solution

Well, int? can be null while int can't. That's why the compiler complains: what should it assign to cid when the query returns null. You can try providing some default value in case of null:

int cid = (  from c in dc.Cs
            where c.id == cid
           select c.clientid)
  .FirstOrDefault() ?? 0; //TODO: put the right default value instead of 0

return cid;

which means return 0 in case of null (please, notice that you have two possibilities: 1. 1st item c.clientid is null; 2. dc.Cs when filtered is empty) and int?.Value otherwise

Related Solutions

C# – How to cast int to enum

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

C# – Get int value from enum in C#

Just cast the enum, e.g.

int something = (int) Question.Role;

The above will work for the vast majority of enums you see in the wild, as the default underlying type for an enum is int.

However, as cecilphillip points out, enums can have different underlying types. If an enum is declared as a uint, long, or ulong, it should be cast to the type of the enum; e.g. for

enum StarsInMilkyWay:long {Sun = 1, V645Centauri = 2 .. Wolf424B = 2147483649};

you should use

long something = (long)StarsInMilkyWay.Wolf424B;

Best Solution

Related Solutions

C# – How to cast int to enum

C# – Get int value from enum in C#

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