<?php
foreach ($_POST['haha'] as $item)
{
echo $item."<br>";
}
?>
<html>
<head>
<body>
<form action="" method="POST">
<input type="checkbox" name="haha[]" value="1">1
<input type="checkbox" name="haha[]" value="2">2
<input type="checkbox" name="haha[]" value="3">3 <br>
<input type="submit" name="btn" value="ok">
</form>
</body>
</head>
</html>