Compilare: main.cpp: In function 'int evaluate(std::__cxx11::string)': main.cpp:38:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < tokens.length(); i++){ ~~^~~~~~~~~~~~~~~~~ main.cpp:58:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < tokens.length() && ~~^~~~~~~~~~~~~~~~~ main.cpp: In function 'int applyOp(int, int, char)': main.cpp:25:1: warning: control reaches end of non-void function [-Wreturn-type] } ^