各位大神帮忙看看哪里错了！
<!DOCTYPE HTML>
<html>
<head>
<meta charset='utf-8'>
<title>计算器</title>
<script type="text/javascript">
function count(){
var a=document.getElementById('txt1').value;
var b=document.getElementById('txt2').value;
var c=document.getElementById('select').value;
var d;
switch(select){
case '+':
d=parseInt(a)+parseInt(b);
break;
case '-':
d=parseInt(a)-parseInt(b);
break;
case '*'：
d=parseInt(a)*parseInt(b);
break;
case '/':
d=parseInt(a)/parseInt(b);
break;
}
document.getElementById('fruit').value=d
}
</script>
</head>
<body>
计算器:<br>
<input type="text" id='txt1'>
<select id='select'>
<option value="+">+</option>
<option value='-'>-</option>
<option value="*">*</option>
<option value="/">/</option>
</select><br>
<input type="text" id='txt2'>
<input type="button" name="button" value="=" onclick='count()'><br>
<input type="text" id='fruit'>
</body>
</html>
