Compilare: user.cpp: In function ‘int main()’: user.cpp:12:20: warning: unused variable ‘j’ [-Wunused-variable] int n,i,firsts,j; ^ user.cpp:13:19: warning: unused variable ‘counter’ [-Wunused-variable] long long int counter=0,s,last; ^ user.cpp:24:28: warning: ‘last’ may be used uninitialized in this function [-Wmaybe-uninitialized] s += 1ll* v[i] * last; ^