Compilare: user.cpp: In function ‘int main()’: user.cpp:15:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(a=1;a<=n;a++) ^ user.cpp:17:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(b=1;b<=n;b++) ^ user.cpp:14:26: warning: unused variable ‘nr’ [-Wunused-variable] unsigned long long d,nr; ^ user.cpp:26:29: warning: ‘d’ may be used uninitialized in this function [-Wmaybe-uninitialized] if(k==1){d++;} ^