Compilare: main.cpp: In function 'void addToString(std::string&, std::string&)': main.cpp:25:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 25 | for (int i = 0; i < s1.size(); ++i) { | ~~^~~~~~~~~~~ main.cpp:31:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 31 | for (int i = 0; i < s1.size(); ++i) { | ~~^~~~~~~~~~~