Compilare: main.cpp: In function 'int get_nr()': main.cpp:17:59: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 17 | while ( expresie[i] >= '0' && expresie[i] <= '9' && i < expresie.size() ) | ~~^~~~~~~~~~~~~~~~~