foo.cc:2:16: error: expected identifier before ';' token
    2 | using namespace;
      |                ^
foo.cc: In function 'int main()':
foo.cc:6:12: error: conflicting declaration 'int x [n2]'
    6 |  int x[n1],x[n2];
      |            ^
foo.cc:6:6: note: previous declaration as 'int x [n1]'
    6 |  int x[n1],x[n2];
      |      ^
foo.cc:6:6: warning: unused variable 'x' [-Wunused-variable]

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