You can say 11

int main()
{
    long long N;
    scanf("%lld",&N);
    while(N)
    {
        if(N%11==0)
            printf("%lld is a multiple of 11.\n",N);
        else printf("%lld is not a multiple of 11.\n",N);
    scanf("%lld",&N);
    }
    return 0;
}