Javasipt: working with the radio tag

1. HTML code:

      <form action="#" name="userOpinionForm" id="userOpinionForm" method="post">
                <input type="radio"    name="opinionCategory" value="1" checked  /> Most agree 
                 <input type="radio"    name="opinionCategory" value="0" /> Most don't agree with 
      </form>

var opinionCategory = document.getElementsByName('opinionCategory');
                 var opinionCategoryValue = 1;
                 for(var i=0;i<opinionCategory.length;i++){
                        if(opinionCategory[i].checked){
                                      opinionCategoryValue = opinionCategory[i].value;
                        }
                 }

var form = document.getElementById('userOpinionForm');
                 var num = 0;
                 for(var i=0;i<form.opinionCategory.length;i++){
                     if(form.opinionCategory[i].checked){
                         num++;
                     }
                 }