Compilare: user.cpp: In function ‘void back(int, int, std::string)’: user.cpp:11:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (a<=b&&s.size()<k){back(a*2,b-a,s+="1\n");} ^ user.cpp:12:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (b<a&&s.size()<k) { back(b*2,a-b,s+="0\n");} ^