Compilare: user.cpp: In function ‘int main()’: user.cpp:19:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<a[pos].size();j++) ^ user.cpp:28:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<a[pos].size();j++) ^ user.cpp:36:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<a[pos].size();j++) ^