Main.cc: In function ‘std::__cxx11::string add(std::__cxx11::string, std::__cxx11::string)’: Main.cc:6:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(a1.size()=0;i--){ ^~ Main.cc:8:12: note: suggested alternative: ‘i’ for(int i=ai.size()-1;i>=0;i--){ ^~ i Main.cc: In function ‘int main()’: Main.cc:19:7: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d,%d",&k,&m); ~~~~~^~~~~~~~~~~~~~~