Compilare: user.cpp: In function ‘int main()’: user.cpp:15:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<n;i++) ~^~ user.cpp:10:34: warning: unused variable ‘l’ [-Wunused-variable] unsigned long long int n,a,b,l=2; ^ user.cpp:11:9: warning: unused variable ‘ok’ [-Wunused-variable] int ok=0; ^~