Compilare: main.cpp: In function 'int main()': main.cpp:53:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 53 | for (int i = 2; i < s.size(); ++i) | ~~^~~~~~~~~~ main.cpp:62:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 62 | for (int i = 2; i < s.size(); ++i) | ~~^~~~~~~~~~ main.cpp:66:38: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 66 | for (int j = (i << 1); j < s.size(); j += i) | ~~^~~~~~~~~~ main.cpp:74:42: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 74 | for (int j = (i << 1); j < s.size(); j += i) | ~~^~~~~~~~~~