Chaine de caracteres dans un attribut d'une balise html

for($i=1;$i<=10;$i++){
  echo "<input type='radio' name='cas".$i."' value='A'><input type='radio' name='cas".$i."' value='B'>";
}

//récupération PROPRE des variables
$arr_cas = !empty($_POST['cas']) ? $_POST['cas'] : NULL;

//traitement du submit
if(!empty($_POST['submit'])){
	foreach($arr_cas as $num=>$K){
		echo "<pre>";
		echo "Cas N°".$num . " => " .$K;		
		echo "<pre>" .PHP_EOL;
	}
	
}


echo "<form method='post' action=''>";

for($i=1;$i<=10;$i++){
  $repASelected = $arr_cas[$i] == 'A' ? 'checked="checked"' : '';
  $repBSelected = $arr_cas[$i] == 'B' ? 'checked="checked"' : '';
  echo "<input type='radio' name='cas[".$i."]' value='A' ".$repASelected."><input type='radio' name='cas[".$i."]' value='B' ".$repBSelected."><br>";
}

echo "<input type='submit' name='submit' value='envoyer'>";
echo "</form>";