Compilare: main.cpp: In function 'void solve(std::__cxx11::string&, std::__cxx11::string&, std::__cxx11::string&)': main.cpp:52:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < first.size() && !valid; i++) ~~^~~~~~~~~~~~~~ main.cpp:61:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < second.size() && !valid; i++) ~~^~~~~~~~~~~~~~~