Checking radio button on submit - PHP - php

Question

I need to check a radio button input on submit.
If none of the radio buttons are checked, $err1_diet gets set to true and the red class needs to be added.
And I also need to know which radio button was checked since this isn't the only question in the form.
if( !isset($_POST['diet']) ){
$err1_diet = true;
}elseif($_POST['diet'] == 1){
$diet = true;
}else{
$diet = false;
$yes = true;
}
<p class="<?php echo (($err1_diet == true) ? "red" : "" ); ?>">• Are you on a diet?<?php var_dump($err1_diet); ?></p>
<input type="radio" name="diet" value="1" <?php echo (($diet) ? 'checked="true"' : "" ); ?> /> Yes
<input type="radio" name="diet" value="0" <?php echo (($diet) ? '' : 'checked="true"' ); ?> /> No

Answer 1

Actually no ... it's checking one of the radio buttons before the form is submitted. That's the problem
You can solve your problem using $_SERVER['REQUEST_METHOD']=='POST' for example:
if( $_SERVER['REQUEST_METHOD']=='POST' and !isset($_POST['diet']) ){
$err1_diet = true;
}elseif($_POST['diet'] == 1){
$diet = true;
}else{
$diet = false;
$yes = true;
}
<p class="<?php echo (($err1_diet == true) ? "red" : "" ); ?>">• Are you on a diet?<?php var_dump($err1_diet); ?></p>
<input type="radio" name="diet" value="1" <?php echo (($diet) ? 'checked="true"' : "" ); ?> /> Yes
<input type="radio" name="diet" value="0" <?php echo (($diet) ? '' : 'checked="true"' ); ?> /> No