Compilare: user.cpp: In function ‘int main()’: user.cpp:16:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( i = 0; i< sir.size()/2 ; ++i ) ^ user.cpp:27:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if( i == sir.size()/2 ) ^ user.cpp:32:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if( i == sir.size() - 1 ) ^