Compilare: user.cpp:8:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^ user.cpp: In function ‘int main()’: user.cpp:12:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j,k,i=s.size()-1; i>=s.size()/2-1; i--) ^ user.cpp:15:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; j>=0 && k<s.size(); j--,k++) ^ user.cpp:18:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k==s.size()-1) x=i; ^ user.cpp:21:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; j>=0 && k<s.size(); j--,k++) ^ user.cpp:24:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k==s.size()-1) x=i; ^