void stars(const unsigned long size)
{
    const unsigned long half = (size + 1) / 2;
    for (long i = 1; i <= size; ++i)
    {
        const unsigned long initspace = (i <= half ? i : size + 1 - i);

        printf("%*c", initspace, '*');
        if (size % 2 == 0 || i != half)
        {
            printf("%*c", size + 1 - initspace * 2, '*');
        }
        putchar('\n');
    }
}