foo.cc: In function ‘int main()’:
foo.cc:7:14: error: ‘setprecision’ was not declared in this scope
    7 | cout<<fixed<<setprecision(6)<<3.141592653589793*R*R<<endl;
      |              ^~~~~~~~~~~~
foo.cc:1: note: ‘std::setprecision’ is defined in header ‘<iomanip>’; this is probably fixable by adding ‘#include <iomanip>’
    1 | #include<iostream>