reference to array is ambiguous error when using memset function

I didn't understand why i take this "strange" error. I read similar questions but it didn't answer my questions. If i define the array inside main function rather than global scope, there is no error. But assume that i have to define this array in global scope. Why do i take this error? Here is the code :

#include <iostream>
#include <cstring>

using namespace std;

int right[1005];
int main()
{
    memset(right,0,sizeof(right));
return 0;
}

Here is the error :

memset2.cpp: In function ‘int main()’:
memset2.cpp:9:9: error: reference to ‘right’ is ambiguous
  memset(right,0,sizeof(right));
     ^
memset2.cpp:6:5: note: candidates are: int right [1005]
 int right[1005];
     ^
In file included from /usr/include/c++/4.8/ios:42:0,
             from /usr/include/c++/4.8/ostream:38,
             from /usr/include/c++/4.8/iostream:39,
             from memset2.cpp:1:
/usr/include/c++/4.8/bits/ios_base.h:924:3: note:                 std::ios_base& std::right(std::ios_base&)
   right(ios_base& __base)
   ^
memset2.cpp:9:24: error: reference to ‘right’ is ambiguous
  memset(right,0,sizeof(right));
                    ^
memset2.cpp:6:5: note: candidates are: int right [1005]
 int right[1005];
     ^
In file included from /usr/include/c++/4.8/ios:42:0,
             from /usr/include/c++/4.8/ostream:38,
             from /usr/include/c++/4.8/iostream:39,
             from memset2.cpp:1:
/usr/include/c++/4.8/bits/ios_base.h:924:3: note:                 std::ios_base& std::right(std::ios_base&)
   right(ios_base& __base)
   ^

Namespace std has already name right and you included names form std in the global namespace by means of directive

using namespace std;

So to avoid the ambiguity use a qualified name

memset( ::right, 0, sizeof( ::right ) );

Or remove the directive and in this case you may use unqualified name right because the compiler will seek the name only in the global namespace.