Compilare: main.cpp: In function 'std::__cxx11::string infixToPostfix(std::__cxx11::string)': main.cpp:18:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ;i<a.size();i++) ~^~~~~~~~~ main.cpp:23:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i<a.size()-1) ~^~~~~~~~~~~ main.cpp: In function 'int solve(std::__cxx11::string)': main.cpp:60:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i<a.size();i++) ~^~~~~~~~~ main.cpp:68:27: warning: unused variable 'res' [-Wunused-variable] int num1,num2,res; ^~~