Compilare: user.cpp: In function ‘int main()’: user.cpp:52:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<b.size();i++) ^ user.cpp:55:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j=0;j<b.size();j++) ^ user.cpp:63:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<b.size();i++) ^