Compilare: main.cpp: In function 'std::__cxx11::string palindrome1(std::__cxx11::string)': main.cpp:36:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) ~~^~~~~~~~~~ main.cpp: In function 'std::__cxx11::string palindrome2(std::__cxx11::string)': main.cpp:46:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) ~~^~~~~~~~~~ main.cpp: In function 'std::__cxx11::string solve(std::__cxx11::string&)': main.cpp:59:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) ~~^~~~~~~~~~