UB can initiate the rise of zombie velociraptors. int n; printf("type 0 to stop the rise of zombie velociraptors"); scanf("%d", &n); realloc(pre, n);

UB can initiate the rise of zombie velociraptors. int n; printf("type 0 to stop the rise of zombie velociraptors"); scanf("%d", &n); realloc(pre, n); if (n != 0) rise_zombie_velociraptors() May result in velociraptors raising even if the user enters "0". The reason is that because realloc(pre, 0) is UB, for the compiler, it cannot happen, so n can't be 0, so the n != 0 test can be optimized out, so, velociraptors.