/in/foo.cc: In function 'int main()':
/in/foo.cc:21:19: warning: too many arguments for format [-Wformat-extra-args]
  printf(".2lf",ans);
                   ^
/in/foo.cc:9:8: warning: unused variable 'j' [-Wunused-variable]
  int i,j,n;
        ^
/in/foo.cc:20:11: warning: 'r' is used uninitialized in this function [-Wuninitialized]
  ans+=3.14*r*2;
       ~~~~^~