.NET namespaces and using statements

What is the difference between

namespace x
{
  using y;
}

and

using y;
namespace x

{
}

?

Answer

The first one has y in scope for just the namespace x, the second has y in scope for the whole file, so potentialy other namespaces. If you keep to one namespace per file (I'd guess that was the convention) then there's usually no real difference [but see Marc's comment about clashes if different types have the same name in different namespaces]. If you use StyleCop it will want you to keep the usings inside the namespace.