Compilare: main.cpp: In function 'int main()': main.cpp:58:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 58 | for (int i = 0; i < expr.length(); ++ i) { | ~~^~~~~~~~~~~~~~~