For loop display radio buttons with first one checked

I have a for loop that displays radio buttons and I want the first one to display as checked. But when I put a if statement inside the for loop for this the page nevers loads. Any ideas?

$mains = array(0=>'Beef Steak', 1=>'Chicken Breast', 2=>'Pork Chops');
$mainscount = count($mains);

<?php for ($mainNO = 0; $mainNO < $mainscount; $mainNO++) { ?>
  <label for="mains<?php echo $mainNO ?>" class="radiobutton"><?php echo $mains[$mainNO]; ?></label>
  <input type="radio" name="mains" id="mains<?php echo $mainNO; ?>" value="<?php echo $mainNO; ?>" 
  <?php if($mainNO = 0){ echo 'checked="checked"'; } ?>/>
<?php } ?>