Compilare: main.cpp: In function 'int main()': main.cpp:18:19: 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 (i = 1; i <= a.size(); i++) | ~~^~~~~~~~~~~ main.cpp:28:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 28 | for (i = 1; i <= a.size(); i++) | ~~^~~~~~~~~~~ main.cpp:32:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 32 | for (i = 1; i <= a.size(); ++i) | ~~^~~~~~~~~~~