运行 ID: 7003

Main.cc: In function ‘int main()’:
Main.cc:5:5: error: ‘cout’ was not declared in this scope
     cout << fixed << setprecision(4) << 2*r;
     ^~~~
Main.cc:5:5: note: suggested alternative:
In file included from Main.cc:1:0:
/usr/include/c++/7/iostream:61:18: note:   ‘std::cout’
   extern ostream cout;  /// Linked to standard output
                  ^~~~
Main.cc:5:13: error: ‘fixed’ was not declared in this scope
     cout << fixed << setprecision(4) << 2*r;
             ^~~~~
Main.cc:5:13: note: suggested alternative:
In file included from /usr/include/c++/7/ios:42:0,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from Main.cc:1:
/usr/include/c++/7/bits/ios_base.h:1041:3: note:   ‘std::fixed’
   fixed(ios_base& __base)
   ^~~~~
Main.cc:5:22: error: ‘setprecision’ was not declared in this scope
     cout << fixed << setprecision(4) << 2*r;
                      ^~~~~~~~~~~~
Main.cc:5:22: note: suggested alternative:
In file included from Main.cc:2:0:
/usr/include/c++/7/iomanip:195:3: note:   ‘std::setprecision’
   setprecision(int __n)
   ^~~~~~~~~~~~