If I compare the counter to five instead of the input (****), then it evaluates perfectly. Thanks to Milo
for the help.
<?php if( have_rows('program_skills') ) :
while( have_rows('program_skills') ) : the_row(); ?>
<div class="skills-wrapper">
<div class="col-xs-6">
<p><?php the_sub_field('heading'); ?></p>
</div>
<div class="col-xs-6">
<div class="skills-graph">
<ul>
****<?php for($i=1; $i<=5; $i+=1)
if( $i <= get_sub_field('rating') ) {
echo '<li class="graph empty ' . 'fill-' . $i . '"></li>';
} else {
echo '<li class="graph empty"></li>';
}
?>
</ul>
</div>
</div>
</div>
<?php endwhile;
endif;?>