Php 对于第一个选中的循环显示单选按钮

我有一个显示单选按钮的for循环，我希望第一个显示为选中状态。但是，当我将if语句放入for循环中时，页面不会加载。有什么想法吗

$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 } ?>

---

您使用=应该使用的位置==

您在比较语句中使用的是assing运算符

<?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";
    } ?>/>

在HTML5中，只能使用checked

//注意：如果条件错误，则使用single=in，它将创建不确定循环。测试代码

<?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";
    } ?>/>

<input type="checkbox" checked>

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

     for ($mainNO = 0; $mainNO < $mainscount; $mainNO++) { 

        // Checked if value is 0
        if($mainNO == 0){  $checked = 'checked="checked"'; }else { $checked =''; };

        echo "<label for='mains".$mainNO."' class='radiobutton'>".$mains[$mainNO]."</label>";
        echo "<input type='radio' name='mains' id='mains".$mainNO."' value='".$mainNO."' $checked   />";


    }