How to substitute a variable in divisibleby?

Question

PHP

Good afternoon. Crashes when executing code

{% set num = (category|length) // 3 %}

<ul class="uList1 ">

    {% for item in category %}
    {% if loop.index is divisibleby(num) %}
        </ul>
        <ul class="uList1 ">
    {% endif %}
    <li><a href="#">{{ item.name }}</a></li>
    {% endfor %}
</ul>

An exception has been thrown during the rendering of a template ("Warning: Division by zero")
Doesn't treat it as a number. number_format also tried. How to be?

Answer 1

probably num=0