foo.cc:2:17: error: expected identifier before 'int'
    2 | using namespace int;
      |                 ^~~
foo.cc:2:16: error: expected ';' before 'int'
    2 | using namespace int;
      |                ^~~~
      |                ;
foo.cc:2:17: error: declaration does not declare anything [-fpermissive]
    2 | using namespace int;
      |                 ^~~
foo.cc: In function 'int main()':
foo.cc:5:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    5 |     cout<<"Hello,world!"<<endl;
      |     ^~~~
      |     std::cout
iostream:61:18: note: 'std::cout' declared here
foo.cc:5:27: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    5 |     cout<<"Hello,world!"<<endl;
      |                           ^~~~
      |                           std::endl
In file included from iostream:39:
/nix/store/1x1q5sqa0ilbi8fz7aayk02pjy5g7jhh-gcc-12.3.0/include/c++/12.3.0/ostream:688:5: note: 'std::endl' declared here
  688 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~

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