提交表单后PHP保持复选框？

I make a user permission form where multiple checkbox exist when i check a checkbox after submitting the form. Form is not showing the previously checked checkbox please help me. I want that form show previously checked checkbox.

Below are the example code of maintain checkbox value after submitting form

<?php
    if (isset($_POST['number']))
    {
        foreach ($_POST['number'] as $selectednumber)
            $selected[$selectednumber] = "checked";
    }
?>

<form action="" method="post">
    <input type="checkbox" name="number[]" <?php echo $selected['one'] ?> value="one" />one<br />
    <input type="checkbox" name="number[]" <?php echo $selected['two'] ?> value="two" />two<br />
    <input type="checkbox" name="number[]" <?php echo $selected['three'] ?> value="three" />three<br />
    <input type="checkbox" name="number[]" <?php echo $selected['four'] ?> value="four" />four<br />
    <input type="submit" name="Submit" value="Submit" />
</form>

So apply on your code and let me know it's helpful or not.