Compilare: user.cpp: In function ‘bool pal(std::string)’: user.cpp:13:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<s.size()/2;i++) ^ user.cpp: At global scope: user.cpp:20:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^ user.cpp: In function ‘int main()’: user.cpp:31:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=n;i<s.size();i++) ^