Compilare: main.cpp: In function 'int valid(std::string)': main.cpp:36:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 36 | for (i = 0; i < s.size(); ++i) | ~~^~~~~~~~~~ main.cpp:33:9: warning: unused variable 'ex' [-Wunused-variable] 33 | int ex=0, maxvf=0; | ^~ main.cpp:33:15: warning: unused variable 'maxvf' [-Wunused-variable] 33 | int ex=0, maxvf=0; | ^~~~~