Compilare: main.cpp: In function 'int eval(std::__cxx11::string)': main.cpp:38:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0 ; i < token.length() ; i++) ~~^~~~~~~~~~~~~~~~ main.cpp:47:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < token.length() && ~~^~~~~~~~~~~~~~~~ main.cpp: In function 'int opera(int, int, char)': main.cpp:29:1: warning: control reaches end of non-void function [-Wreturn-type] } ^