JS从单选框中选择一个值后,点击提交后显示出该值!请问我的代码怎么修改啊啊?

 <head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script type="text/javascript" language="javascript">
    var cake_prices = new Array();
    cake_prices["Round6"]=20;
    cake_prices["Round8"]=25;
    cake_prices["Round10"]=35;
    cake_prices["Round12"]=75;
    function getCakeSizePrice() {
        var cakeSizePrice=0;
        var theForm=document.forms["myForm"];
        var selectedCake = document.getElementsByName("selectedcake");
        for(var i = 0; i < selectedCake.length; i++) {
            if(selectedCake[i].checked) {
                var cakeSizePrice = cake_preces[selectedCake[i].value];
                break;
            }
        }
        alert("价格是"+parseInt(cakeSizePrice));
    }
</script>

</head>

<body>
<form name="myForm" >
<label> 1)选一个正确的</label><br />
<input type="radio"  name="selectedcake" id="roud6" value="Round6"
  />
    Round cake 6" -  serves 8 people ($20)<br />
<input type="radio"  name="selectedcake" id="round8" value="Round8"
   />
    Round cake 8" - serves 12 people ($25)<br />
<input type="radio"  name="selectedcake" id="round10" value="Round10" />
    Round cake 10" - serves 16 people($35)<br />
<input type="radio"  name="selectedcake" id="round12" value="Round12"/>
    Round cake 12" - serves 30 people($75)<br />
<input type="button"  value="提交" name="area" onclick="getCakeSizePrice()"/>
</form>
</body>

变量名错了

 var cakeSizePrice = cake_preces[selectedCake[i].value];

===>

 var cakeSizePrice = cake_prices[selectedCake[i].value];