Compilare: user.cpp: In function ‘int main()’: user.cpp:22:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<c[a].size();++j) ^ user.cpp:29:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<c[b].size();++j) ^ user.cpp:37:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<c[a].size();++j) ^