PHP loop to echo certain div class on first round only - php

Question

I'm trying to create an accordion where the first one is open (with this CSS that means that the panel has 'in' added to the panel-collapse div).
So, I'm setting the variable $i to 1 and just echoing 'in' when it does equal 1, incrementing after the first. When this is executed, however, all looped posts have 'in' and so are open. Can anyone see what I'm doing wrong?
<?php
$i=1;
while ( $loop->have_posts() ) : $loop->the_post(); ?>
<!-- individual panel -->
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" data-parent="#faqs" href="#<?php the_ID(); ?>">
<?php the_title(); ?>
</a>
</h4>
</div>
<div id="<?php the_ID(); ?>" class="panel-collapse collapse <?php if ($i=1) { echo 'in'; } ?>">
<div class="panel-body">
<?php the_field('answer'); ?>
</div>
</div>
</div>
<!-- /individual panel -->
<?php $i++; endwhile;
?>

Answer 1

<?php
$i=1;
while ( $loop->have_posts() ) : $loop->the_post(); ?>
<!-- individual panel -->
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" data-parent="#faqs" href="#<?php the_ID(); ?>">
<?php the_title(); ?>
</a>
</h4>
</div>
<div id="<?php the_ID(); ?>" class="panel-collapse collapse <?php if ($i==1) { echo 'in'; } ?>">
<div class="panel-body">
<?php the_field('answer'); ?>
</div>
</div>
</div>
<!-- /individual panel -->
<?php $i++; endwhile;
?>
It should be $i==1 not $i=1 in your if condition
When you do $i=1 it means you are assigning value 1 to $i , so every time it is successfully satisfying condition.
Here is Comparison Operators :D