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                        /JavaScript進階篇

出不來結(jié)果，求解？？？

function count(){
????? var a=document.getElementById("txt1").value;
????? var b=document.getElementById("txt2").value;
???? ?
????? a=parselnt(a);
????? b=parselnt(b);
????? var c=document.getElementById("select").value;
????? var d;
????? switch(c){
????????? case "+":d=a+b;break;
????????? case "-":d=a-b;break;
????????? case "*":d=a*b;break;
????????? case "/":d=a/b;break;
????????? default:
????? }
????? document.getElementById("fruit").value=d;
?? }
? </script>
?</head>
?<body>
?? <input type='text' id='txt1' />
?? <select id='select'>
?? ??? ?<option value='+'>+</option>
?? ??? ?<option value="-">-</option>
?? ??? ?<option value="*">*</option>
?? ??? ?<option value="/">/</option>
?? </select>
?? <input type='text' id='txt2' />
?? <input type='button' value=' = ' onclick="count()"/> 
?? <input type='text' id='fruit' />??