Compilare: user.cpp: In function ‘std::__cxx11::string solve(const string&)’: user.cpp:29:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ user.cpp:19:6: warning: unused variable ‘fmax’ [-Wunused-variable] int fmax, nrmax, i, j, n, ch; ^~~~ user.cpp:19:12: warning: unused variable ‘nrmax’ [-Wunused-variable] int fmax, nrmax, i, j, n, ch; ^~~~~