Compilare: main.cpp: In member function 'std::vector<std::__cxx11::basic_string<char> > Expression::createPostfixExpression()': main.cpp:64:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < infixExpression.length(); i++) { ~~^~~~~~~~~~~~~~~~~~~~~~~~~~ main.cpp:69:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; i < infixExpression.length() && (isdigit(infixExpression[i]) || infixExpression[i] == '.'); i++) { ~~^~~~~~~~~~~~~~~~~~~~~~~~~~