Compilare: user.cpp: In function ‘int main()’: user.cpp:22:15: warning: variable ‘x’ set but not used [-Wunused-but-set-variable] for (auto x : next_char) ^ user.cpp:24:15: warning: variable ‘x’ set but not used [-Wunused-but-set-variable] for (auto x : extind) ^ user.cpp:40:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = s.size() - 1; i > s.size() - 1 - l; -- i) ~~^~~~~~~~~~~~~~~~~~ user.cpp:75:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = l - 1; i < s.size(); ++ i){ ~~^~~~~~~~~~