Hi guys I have created a form that has checkboxes, the code works great when a checkbox is selcted however when no checkboxes are selected I get errors such as "Undefined index: onemon in and Warning: Invalid argument supplied for foreach()" Please help:)

FORM

1. Had a cold, fever or headache? input type="checkbox" name="onemon[]" value="q1"
if(isset($_GET['onemon']) && $_GET['onemon']= "q1")

2. Had dental extractions or teeth cleaning? input type="checkbox" name="onemon[]" value="q2" if(isset($_GET['onemon']) && $_GET['onemon']= "q2")

3. Had minor outpatient sugery? input type="checkbox" name="onemon[]" value="q3" if(isset($_GET['onemon']) && $_GET['onemon']= "q3")

4. Had any vaccines? input type="checkbox" name="onemon[]" value="q4" if(isset($_GET['onemon']) && $_GET['onemon']= "q4")

PHP

$date = date('Y-m-d'); 
$onemon = $_POST ['onemon'];

{ $con = mysql_connect("localhost","root","") or die ("Could not connect to DB Server");
     $db_selected = mysql_select_db("nbtsdb", $con) or die("Could not locate the DB"); 


     // You have to loop through the array of checked box values ... 

$ques=""; foreach($onemon as $entry){ $ques .= $entry.","; }

     //$addPersonalSql holds the insert SQL query string
     $query = "INSERT INTO defferal(defid, intdate, onemonth)
         VALUES('','$date','$ques')";
     $addMemberSql = $query or die ("Unable to Insert Data into defferal Table");
        mysql_query($addMemberSql);

     }