Compilare: main.cpp: In function 'std::__cxx11::string add(std::__cxx11::string, std::__cxx11::string)': main.cpp:183:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s2.length(); i ++) ~~^~~~~~~~~~~~~ main.cpp:190:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(carry && idx < s1.length()) ~~~~^~~~~~~~~~~~~