Compilare: main.cpp: In member function 'int ExprEvaluator::Evaluate(std::__cxx11::string)': main.cpp:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < expr.size(); ++i) { ~~^~~~~~~~~~~~~ main.cpp:15:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i + 1 < expr.size() && isDigit(expr[i + 1])) { ~~~~~~^~~~~~~~~~~~~