Compilare: main.cpp: In function 'int main()': main.cpp:56:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 56 | for(int i=0; i<a.size(); ++i) | ~^~~~~~~~~ main.cpp:60:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 60 | for(int i=0; i<b.size(); ++i) | ~^~~~~~~~~ main.cpp:64:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 64 | for(int i=0; i<c.size(); ++i) | ~^~~~~~~~~