Check Boxes and updating records. (HELP ME....)

OK, I've a page for my users to sign up on my website and in the form, there's a few checkboxes fields. So I set the name of the check boxes as name[] and PHP made an array of all the options choosen. All the check boxes values are numbers, so I got all the numbers from the array, put a comma between them all and inserted them as one field in my database. Easy. It worked well. But now I've a problem. I want to give users the option of changing their details when they log into the site. So I get the form and put <?php echo $variable_name; ?> in every text box so the user sees their record. I had a small problem with showing choosen values in dropdown lists and radio options but i solved them both. But I cannot think of any way to show what check boxes were choosen by the user. Could anyone help me? PLEASE