function count(){
var a = document.getElementById("txt1").value;
var b = document.getElementById("txt2").value;
var c;
switch(select)
case "+":
c = a + b;
break;
case "-":
c = a - b;
break;
case "*":
c = a * b;
break;
case "/":
c = a / b;
break;
document.getElementById("fruit").value = c;
2015-12-28
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
//获取第一个输入框的值
var val1 = document.getElementById("txt1").value;
//获取第二个输入框的值
var val2 = document.getElementById("txt2").value;
//获取选择框的值
var selectval = document.getElementById("select").value;
//获取通过下拉框来选择的值来改变加减乘除的运算法则
var result; //定义一个变量，接收值
switch(selectval){
case "+":
result = parseFloat(val1) + parseFloat(val2);
break;
case "-":
result = parseFloat(val1) - parseFloat(val2);
break;
case "*":
result = parseFloat(val1) * parseFloat(val2);
break;
case "/":
if(parseFloat(val1) == 0 && parseFloat(val2) == 0){
alert("0不能与0相除");
}else if(parseFloat(val2) == 0){
alert("除数不能为0");
}else{
result = parseFloat(val1) / parseFloat(val2);
}
break;
}
//设置结果输入框的值
document.getElementById("fruit").value = result; //把result赋值给结果输入框
}
</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();"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' onfocus ="count();"/> <!--通过焦点来得出答案-->
</body>
</html>
举报
