<body>
<input id="ice">
<select id="mum">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input id="box1">
=<input id="result">
<button οnclick="bule()">计算</button>
<script>
function bule() {
var num1 =parseFloat(document.getElementById("ice").value);
var num2 = parseFloat(document.getElementById("box1").value);
var num3 = document.getElementById("mum").value;
var number3;
if(num3=="+"){
number3 = num1 + num2;
}else if (num3=="-"){
number3 = num1 - num2;
}else if (num3=="*"){
number3 = num1*num2;
}else if(num3=="/"){
number3 = num1/num2;
}
document.getElementById('result').value = number3;
}
</script>
</body>