/in/foo.cc: In function 'int main()':
/in/foo.cc:6:46: warning: format '%lf' expects argument of type 'double', but argument 2 has type 'int' [-Wformat=]
  printf("%.4lf %.4lf %.4lf",2*n,2*n*pi,n*n*pi);
                                              ^
/in/foo.cc:6:46: warning: format '%lf' expects argument of type 'double', but argument 3 has type 'int' [-Wformat=]
/in/foo.cc:6:46: warning: format '%lf' expects argument of type 'double', but argument 4 has type 'int' [-Wformat=]