自动累加checked的checkbox的value
DOM:     
  <form>  
  <table>  
  <tbody>  
  <tr>  
 	 <td> sample </td>  
 	 <td   class= "trade_price "> 100.80 </td>  
 	 <td>  <input   type= "checkbox "   name= "trade_picker "/>  </td>  
  </tr>  
  <tr>  
 	 <td> sample </td>  
 	 <td   class= "trade_price "> 49.72 </td>  
 	 <td>  <input   type= "checkbox "   name= "trade_picker "/>  </td>  
  </tr>  
  <tr>  
 	 <td> sample </td>  
 	 <td   class= "trade_price "> 122.50 </td>  
 	 <td>  <input   type= "checkbox "   name= "trade_picker "/>  </td>  
  </tr>  
  <tr>  
 	 <td> sample </td>  
 	 <td   class= "trade_price "> 95.00 </td>  
 	 <td>  <input   type= "checkbox "   name= "trade_picker "/>  </td>  
  </tr>  
  <tr>  
 	 <td> sample </td>  
 	 <td   class= "trade_price "> 8.00 </td>  
 	 <td>  <input   type= "checkbox "   name= "trade_picker "/>  </td>  
  </tr>  
  </tbody>  
  </table>  
  <p> total: <input   type= "text "   id= "total_price "   value= "0.00 "/>  </p>  
  <button> submit </button>  
  </form>    
 在每次改变.trade_picker的时候,#total_price的value会重新累加,请高手赐教。
------解决方案-------------------- <input type= "checkbox " name= "trade_picker " onchange= "Add(要相加的值,this) "/>    
  <script>  
 function Add(value,cb) 
 { 
   var price=document.getElementById( 'total_price '); 
   if(cb.checked) 
    price.value=parseInt(price.value)+parseInt(value); 
   else 
    price.value=parseInt(price.value)-parseInt(value); 
 } 
  </script>
------解决方案--------------------我只能写成这样了。有点不对 。。。 
  <!DOCTYPE html PUBLIC  "-//W3C//DTD XHTML 1.0 Transitional//EN "  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">  
  <html xmlns= "http://www.w3.org/1999/xhtml ">  
  <head>  
  <meta http-equiv= "Content-Type " content= "text/html; charset=gb2312 " />  
  <title> 无标题文档 </title>    
  <script language= "javascript ">  
 	function add() 
 	{ 
 		var src=event.srcElement; 
 		var total=document.getElementById( "total_price ");  		  	 
 		if (src.checked) 
 		{ 
 			total.value=parseFloat(total.value)+parseFloat(src.parentNode.previousSibling.innerHTML); 
 		}else{ 
 			total.value=parseFloat(total.value)-parseFloat(src.parentNode.previousSibling.innerHTML); 
 		} 
 	}   
 	function onload() 
 	{ 
 		var inputarr=document.getElementsByName( "trade_picker "); 
 		for (var i=0;i <inputarr.length;i++ ) 
 		{ 
 			inputarr[i].attachEvent( "onclick ",add); 
 		} 
 	} 
  </script>  
  </head>    
  <body onload= "onload() ">  
  <form>  
  <table>  
  <tbody>  
  <tr>  
 	 <td> sample </td>  
 	 <td class= "trade_price "> 100.80 </td>  
 	 <td>  <input ty