Why GetType returns System.Int32 instead of Nullable? [duplicate]

Answer 1

Because the type of "5" is int.

If you want to detect if a type is nullable, and the underlying type, use something like this:

public static Type GetActualType(Type type, out bool isNullable)
{
    Type ult = Nullable.GetUnderlyingType(type);
    if (ult != null)
    {
        isNullable = true;
        return ult;
     }
     isNullable = false;
     return type;
}