/in/foo.cc: In function 'int main()':
/in/foo.cc:25:2: error: 'cin' was not declared in this scope
cin>>n;
^~~
/in/foo.cc:25:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/7/iostream:60:18: note: 'std::cin'
extern istream cin; /// Linked to standard input
^~~
/in/foo.cc:28:2: error: 'cout' was not declared in this scope
cout<<sum;
^~~~
/in/foo.cc:28:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/7/iostream:61:18: note: 'std::cout'
extern ostream cout; /// Linked to standard output
^~~~