Compilare: user.cpp: In function ‘void df2(int)’: user.cpp:26:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (++a[x][0]<a[x].size()) ^ user.cpp: In function ‘int main()’: user.cpp:59:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (++a[x][0]<a[x].size()) ^ user.cpp:69:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (a[x][0]>=a[x].size()) ^