foo.cc: In function 'int main()':
foo.cc:8:2: error: 'cin' was not declared in this scope
  cin>>dan1;
  ^~~
foo.cc:8:2: note: suggested alternative:
In file included from foo.cc:2:0:
/usr/include/c++/6/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
foo.cc:16:2: error: 'cout' was not declared in this scope
  cout<<fixed<<setprecision(2);
  ^~~~
foo.cc:16:2: note: suggested alternative:
In file included from foo.cc:2:0:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~
foo.cc:16:8: error: 'fixed' was not declared in this scope
  cout<<fixed<<setprecision(2);
        ^~~~~
foo.cc:16:8: note: suggested alternative:
In file included from /usr/include/c++/6/iomanip:40:0,
                 from foo.cc:1:
/usr/include/c++/6/bits/ios_base.h:1041:3: note:   'std::fixed'
   fixed(ios_base& __base)
   ^~~~~
foo.cc:16:29: error: 'setprecision' was not declared in this scope
  cout<<fixed<<setprecision(2);
                             ^
foo.cc:16:29: note: suggested alternative:
In file included from foo.cc:1:0:
/usr/include/c++/6/iomanip:195:3: note:   'std::setprecision'
   setprecision(int __n)
   ^~~~~~~~~~~~

自豪的采用jd5进行评测(github.com/masnn/jd5)