/in/foo.cc: In function 'int main()':
/in/foo.cc:6:2: error: 'cin' was not declared in this scope
  cin>>n;
  ^~~
/in/foo.cc:6:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
/in/foo.cc:6:7: error: 'n' was not declared in this scope
  cin>>n;
       ^
/in/foo.cc:9:7: error: expected ';' before 'a'
   cin a[i];
       ^
/in/foo.cc:11:12: error: 'sort' was not declared in this scope
  sort(a,a+n);
            ^
/in/foo.cc:11:12: note: suggested alternative:
In file included from /usr/include/c++/6/algorithm:62:0,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/stl_algo.h:4727:5: note:   'std::sort'
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
     ^~~~
/in/foo.cc:12:2: error: 'cout' was not declared in this scope
  cout<<a[n-1];
  ^~~~
/in/foo.cc:12:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~