Compilare: user.cpp: In function ‘std::__cxx11::string reversepolishnotation(std::__cxx11::string)’: user.cpp:45:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s.size(); i++) ~^~~~~~~~~ user.cpp: In function ‘bool value(std::__cxx11::string)’: user.cpp:84:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s.size(); i++) ~^~~~~~~~~ user.cpp: In function ‘bool egal(std::__cxx11::string, std::__cxx11::string)’: user.cpp:128:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s1.size(); i++) ~^~~~~~~~~~ user.cpp:131:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s2.size(); i++) ~^~~~~~~~~~ user.cpp: In function ‘int val(int, int, char)’: user.cpp:40:1: warning: control reaches end of non-void function [-Wreturn-type] } ^