Compilare: main.cpp: In function 'std::istream& operator>>(std::istream&, Nr&)': main.cpp:82:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0, act = -1, p; i < s.size(); i++, p *= 10) { ~~^~~~~~~~~~ main.cpp:82:35: warning: 'p' may be used uninitialized in this function [-Wmaybe-uninitialized] for (int i = 0, act = -1, p; i < s.size(); i++, p *= 10) { ^