Compilare: main.cpp: In function 'int main()': main.cpp:44:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 44 | for (int i = 0; i < s.size(); i++) | ~~^~~~~~~~~~ main.cpp: In function 'int pr(char)': main.cpp:19:1: warning: control reaches end of non-void function [-Wreturn-type] 19 | } | ^ main.cpp: In function 'int op(int, char, int)': main.cpp:34:1: warning: control reaches end of non-void function [-Wreturn-type] 34 | } | ^