Compilare: user.cpp: In function ‘int main()’: user.cpp:22:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 1; i < a.length() && sol.size() < 1000; i++) { ^ user.cpp:32:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < sol.size(); i++) ^