Compilare: user.cpp: In function ‘int main()’: user.cpp:33:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (a = 0; a < graph[i].size(); ++a) ^ user.cpp:45:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < graph[a].size(); ++i) ^ user.cpp:53:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0; j < graph[a].size(); ++j) ^