foo.cc: In function 'int main()':
foo.cc:3:5: error: 'cout' was not declared in this scope
     cout<<1;
     ^~~~
foo.cc:3:5: note: suggested alternative:
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:75:0,
                 from foo.cc:1:
/usr/include/c++/7/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。