Compilare: user.cpp: In function ‘std::istream& operator>>(std::istream&, bigint&)’: user.cpp:15:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();i++) ^ user.cpp: In function ‘std::ostream& operator<<(std::ostream&, bigint&)’: user.cpp:22:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<x.size();i++) ^ user.cpp: In function ‘bigint operator+(const bigint&, const bigint&)’: user.cpp:34:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<z.size();i++){ ^