</head>
<div>
<input id="t1" type="text">
<select id="c1">
<option value="+" selected>+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
<option value="%">%</option>
</select>
<input id="t2" type="text">
<input id="btn" type="button" value="=">
<input id="t3" type="text" disabled>
</div>
<body>
</body>
<script>
var t1 =document.getElementById("t1");
var t2 =document.getElementById("t2");
var t3 =document.getElementById("t3");
var c1 = document.getElementById("c1");
var btn =document.getElementById("btn");
btn.onclick = function(){
var num1 = Number(t1.value);
var num2 = Number(t2.value);
no(num1,num2,c1.value);
}
function no(num1, num2, c1) {
var num = 0;
if(num1==""||num2==""){
alert("您的输入有误！")
}else{
switch (c1) {
case "+":
num = num1 + num2;break;
case "-":
num = num1 - num2;break;
case "*":
num = num1 * num2;break;
case "/":
num = num1 / num2;break;
case "%":
num = num1 % num2;break;
}
t3.value = num ;
}
}
</script>
