Compilare: main.cpp: In function 'int main()': main.cpp:18:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 18 | for (int i = 0; i < s.size(); i++) | ~~^~~~~~~~~~ main.cpp:22:22: warning: array subscript has type 'char' [-Wchar-subscripts] 22 | f[st.back()] = i; | ~~~~~~~^~ main.cpp:29:18: warning: array subscript has type 'char' [-Wchar-subscripts] 29 | f[st.back()] = s.size(); | ~~~~~~~^~ main.cpp:33:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 33 | for (int i = 0; i < s.size(); i++) | ~~^~~~~~~~~~