Compilare: user.cpp: In function ‘bool grad2(std::string)’: user.cpp:51:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0 ; i < s.size() ; i++) ^ user.cpp: In function ‘void solve2(std::string)’: user.cpp:90:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < s.size()){ ^ user.cpp: In function ‘void solve1(std::string)’: user.cpp:154:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < s.size()) ^