/in/foo.cc: In function 'std::__cxx11::string ADD_INT(std::__cxx11::string, std::__cxx11::string)':
/in/foo.cc:55:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
                 for (i=1;i<=L2-L1;i++) str1="0"+str1;
                          ~^~~~~~~
/in/foo.cc:57:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
                 for (i=1;i<=L1-L2;i++) str2="0"+str2;
                          ~^~~~~~~