Possible Duplicate:
Should Usings be inside or outside the namespace
What is the difference between
namespace x
{
using y;
}
and
using y;
namespace x
{
}
?
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.
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