Compilare: main.cpp: In function 'int main()': main.cpp:11:15: warning: unused variable 'n' [-Wunused-variable] long long n,k,i,j,ok=1; ^ main.cpp:19:15: warning: iteration 999998 invokes undefined behavior [-Waggressive-loop-optimizations] a[2*i]=1; ~~~~~~^~ main.cpp:18:16: note: within this loop for (i=2; i<=1000000; i++) ~^~~~~~~~~ main.cpp:15:13: warning: iteration 999999 invokes undefined behavior [-Waggressive-loop-optimizations] a[i]=0; ~~~~^~ main.cpp:13:16: note: within this loop for (i=2; i<=2000000; i=i+2) ~^~~~~~~~~