/in/foo.cc: In function 'int output(int)':
/in/foo.cc:9:10: warning: unused variable 'x' [-Wunused-variable]
      int x=0;
          ^
/in/foo.cc:25:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:36:18: error: 'endl' was not declared in this scope
     std::cout << endl;
                  ^~~~
/in/foo.cc:36:18: note: suggested alternative:
In file included from /usr/include/c++/6/iostream:39:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/ostream:590:5: note:   'std::endl'
     endl(basic_ostream<_CharT, _Traits>& __os)
     ^~~~