Compilare: main.cpp: In function 'std::__cxx11::string infixToPostFix(std::__cxx11::string)': main.cpp:29:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i< a.size(); i++) ~^~~~~~~~~~ main.cpp:34:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i!=a.size()-1) ~^~~~~~~~~~~~ main.cpp: In function 'long long int solvePostFix(std::__cxx11::string)': main.cpp:72:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i<a.size();i++) ~^~~~~~~~~