Twig rule for alternating between two div classes

Question

First of all, I'm not a programmer/web designer, and I'm just making a small fan site, so I'm sorry if it seems that I put too little effort in trying to do this myself.

Basically, I'm trying to modify a site template in a way so it would show news thumbnails not just on the right side of the article preview, but would alternate between left and right. The template uses HTML, CSS, and Twig. imageholder-right and imageholder-left are valid CSS classes.

This is how it originally was:

        {% if record.image!="" %}
            <div class="large-4 imageholder-right">
                <a href="{{ image(record.image) }}">
                    <img src="{{ thumbnail(record.image, 400, 260) }}">
                </a>
            </div>
        {% endif %}

This is what I attempted to do so it could function like I want to:

        {% if record.image!="" %}
            {% set imagepos = 'right' %}
            {% if imagepos == right %}
                <div class="large-4 imageholder-left">
                    <a href="{{ image(record.image) }}">
                        <img src="{{ thumbnail(record.image, 400, 260) }}">
                    </a>
                </div>
                {% set imagepos = 'left' %}
            {% else %}
                <div class="large-4 imageholder-right">
                    <a href="{{ image(record.image) }}">
                        <img src="{{ thumbnail(record.image, 400, 260) }}">
                    </a>
                </div>  
                {% set imagepos = 'right' %}
            {% endif %}
        {% endif %}

However, with this code every image preview remains on the right.

Answer 1

You could give a look at {% loop.index %}.

Twig - Loops

I guess your code is in a loop?

Edit:

As @DarkBee suggested, the cleanest way is to use <div class="large-4 imageholder-{{ loop.index is even ? 'right' : 'left' }}">.

{% for record in records %}
    {% if record.image != "" %}
        <div class="large-4 imageholder-{{ loop.index is even ? 'right' : 'left' }}">
            <a href="{{ image(record.image) }}">
                <img src="{{ thumbnail(record.image, 400, 260) }}">
            </a>
        </div>
    {% endif %}
{% endfor %}