In file included from /usr/include/c++/9/backward/strstream:50,
                 from /in/foo.cc:3:
/usr/include/c++/9/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated. [-Wcpp]
   32 | #warning \
      |  ^~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:12:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |         for(int i=0;i<n.length();i++)
      |                     ~^~~~~~~~~~~