Compilare: main.cpp: In function 'std::vector<std::__cxx11::basic_string<char> > transform_to_postfix(std::__cxx11::string)': main.cpp:18:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < S.size(); i++) ~~^~~~~~~~~~ main.cpp:23:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i + 1 < S.size() && S[i + 1] >= '0' && S[i + 1] <= '9') ~~~~~~^~~~~~~~~~ main.cpp: In function 'int convert_string_to_number(std::__cxx11::string)': main.cpp:65:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < S.size(); i++) ~~^~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:100:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("evaluare.in", "r", stdin); ^ main.cpp:101:41: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("evaluare.out", "w", stdout); ^ main.cpp: In function 'int evaluate(std::vector<std::__cxx11::basic_string<char> >)': main.cpp:83:17: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized] int res; ^~~