selecting checkboxes are not checking respective texboxes empty or not

My problem is selecting checkboxes are not checking respective texboxes empty or not in javascript. Here is my javascript code:

function check(xform)
{ 
var chkedBoxes = [], i = 0, inputs = document.xform.getElementsByTagName('input');
 while (i<9) 
       {
  if (inputs[i].type == 'checkbox' && inputs[i].checked && document.xform.quantity[i].value=="" )
   {
   	 alert('specify the quantity');
     return false;	
   }
	i++;
        }
   }

Code (markup):

My checkboxes are here moving in a loop:
<input type="checkbox" name="chkID[]" id="chkID[]" value="<?=$rowSubjectsx['ID']?>">
And my text boxes are also moving in a loop:
<input type="text" name="quantity[]" id="quantity[]" size="3"/>
Please Help...