PHP获取多选框的值

< input type="checkbox" name="weeks[]" 
id="weeks" value=1>    
< input type="checkbox" name="weeks[]" 
id="weeks" value=2>    
< input type="checkbox" name="weeks[]" 
id="weeks" value=3>

<?
$weeks = $_POST['weeks'];
for($i=0;$i< count($weeks);$i++){
   echo $weeks[1]."< br>";  
}
?>