Compilare: user.cpp: In function ‘int main(int, const char**)’: user.cpp:21:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < str.length(); i ++ ) { ^ user.cpp:27:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] out << ( ( l == str.length() - 1 ) ? "DA" : "NU" ) << endl; } ^