Compilare: user.cpp: In function ‘void topo(int)’: user.cpp:15:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<a[x].size();i++) ^ user.cpp: In function ‘int main()’: user.cpp:50:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j=0;j<a[nr].size();j++) ^ user.cpp:60:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j=0;j<a2[nr].size();j++) ^