How to handle twig view and bootstrap 3 rows/columns?

Question

I have an Article entity and I made a findAll() in the controller.

I rendered each article in a div with the col-md-6 class.

But foreach 2 articles I must wrap these divs in a row div.

How can I do this with twig ?

Thanks.

EDIT :

I tried your code (NHG) like this:

{% for article in articles %}
    {% if loop.index % 2 == 0 %}
        <div class="row"></div>
    {% endif %}
    <div class="col-md-6">
        <article class="well well-sm">
            <a href="#"><img src="{{ article.image }}" alt="{{ article.title }}" class="img-thumbnail"></a>
            <h2 class="h3 text-center"><a href="#">{{ article.title }}</a></h2>
            <div class="alert alert-success well-sm">
                {{ article.content|striptags|slice(0, 235) }}...
            </div>
            <a class="btn btn-default btn-sm pull-right" href="#">{{ article.comments|length }} Comments</a>
            <div class="btn-group btn-group-sm">
                {% for tag in article.tags %}
                    <a class="btn btn-default">{{ tag.name }}</a>
                {% endfor %}
            </div>
        </article>
    </div>
{% endfor %}

But it doesn't work.

I want to have something like this :

<div class="row">
    <div class="col-md-6"></div>
    <div class="col-md-6"></div>
</div>

<div class="row">
    <div class="col-md-6"></div>
    <div class="col-md-6"></div>
</div>

<div class="row">
    <div class="col-md-6"></div>
    <div class="col-md-6"></div>
</div>

Answer 1

UPDATED:

As @Maerlyn suggested:

{% for row in articles|batch(2) %}
    <div class="row">
        {% for article in row %}
            <div class="col-md-6">
                // your content
            </div>
        {% endfor %}
    </div>
{% endfor %}

OLD way:

Use loop.index (doc: The loop variable), modulo (doc: Math operators) and if (doc: if statement )

{% for article in articles %}
    {% if loop.index % 2 == 1 %}
        <div class="row">
    {% endif %}
    <div class="col-md-6">
        // your content
    </div>
    {% if (loop.index % 2 == 0 or loop.last) %}
        </div>
    {% endif %}
{% endfor %}