php and forms

hi, I am very new to php so please forgive me if this is somewhat of a dumb question I have a html page with a whole bunch of textfields and checkboxes. Once the user fills out the information it is entered it is recorded in a mySQL db/table the problem that i am having is with the checkboxes. if they are checked everything works fine, but if they are not then I get this: Notice: Undefined index: foo how do I make this notice disappear?