Compilare: user.cpp: In function ‘void back(int)’: user.cpp:25:12: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if (nr1+nr2==N && sum1+sum2==H) ^ user.cpp: In function ‘void extrage(std::string&, int)’: user.cpp:76:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<v.size();++i) ^ user.cpp: In function ‘int main()’: user.cpp:97:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<S.size();++i) ^