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实例

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>jisuanqi</title>
	<style type="text/css" media="screen">
			.box {
			width: 500px;
			height: 200px;
			background-color: #efefef;
			border: 1px solid lightgray;
			text-align: center;
			margin: auto;
			margin: 20px auto;
			color: #636363;
			border-radius: 15px;
			box-shadow: 2px 2px 2px #999;
		}

		table {
			margin: auto;
			/*border: 1px solid red;*/
		}

		td {
			width: 100px;
			height: 30px;
			padding: 5px 10px;
		}

		input, select {
			width: 100%;
			height:100%;
			border:none;
			text-align: center;
			/*background-color: cyan;*/
		}

		button {
			width: 100%;
			height: 100%;
			border: none;
			background-color: skyblue;
			color: white;
		}
		button:hover {
			cursor: pointer;
			background-color: coral;
			width: 105%;
			height: 105%;
		}

	</style>
</head>
<body>
<div class="box">		

<table>
	<caption>计算器运算表</caption>
	<thead>
		<tr>
			<th> </th>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td><input type="text" name="opt1"  placeholder="第一个数字"></td>

			<td><select name="option" >
				<option value="null">请选择运算符</option>
			    <option value="add"> + </option>
			    <option value="sub"> - </option>
			    <option value="mul"> * </option>
			    <option value="div"> / </option>
			
			</select></td>

			<td><input type="text" name="opt2"  placeholder="第二个数字"></td>

			<td><button type="button">计算</button></td>
				</tr>
				<tr>
					<td colspan="2" ><h3>结果:</h3></td>
					<td colspan="2"><h3 id="placeholder"></h3></td>
				</tr>

			
		</tr>
	</tbody>
</table>
</div>
<script type="text/javascript">
		//1.获取操作数,按钮与结果占位符
		var opt1 = document.getElementsByName('opt1')[0]
		var opt2 = document.getElementsByName('opt2')[0]
		var opt  = document.getElementsByName('option')[0]

		var btn = document.getElementsByTagName('button')[0]
		var placeholder = document.getElementById('placeholder')

		
		//2.给按钮添加事件,执行计算操作
		btn.onclick = function(){
			// var data1 = parseFloat(opt1.value)
			// var data2 = parseFloat(opt2.value)


			if (opt1.value.length == 0 ) {
				alert('第一个操作数不能为空')
				opt1.focus()
				return false
			} else if (isNaN(opt1.value)) {
				alert('第一个操作数必须为数字')
				opt1.focus()
				return false
			} else if (opt2.value.length == 0) {
				alert('第二个操作数不能为空')
				opt2.focus()
				return false
			} else if (isNaN(opt2.value)) {
				alert('第二个操作数必须为数字')
				opt2.focus()
				return false
			} else {
				var data1 = parseFloat(opt1.value)
				var data2 = parseFloat(opt2.value)
			}
			

			var option  = opt.value
			var temp = 0
			var flag = ''
			var result = ''
			switch (option){
				case 'null':
					alert("请选择操作类型")
					opt.focus()
					return false
				case 'add':
					flag = '+'
					temp = data1 + data2					
					break
				case 'sub':
					flag = '-'
					temp = data1 - data2
					break
				case 'mul':
					flag = '*'
					temp = data1 * data2
					break
				case 'div':
					flag = '/'
					if (data2 == 0) {
						alert('除数不能为0,请重新输入')
						opt2.focus()
						return false
					} else {
						temp = data1 / data2	
					}					
					break
			}

			 placeholder.innerHTML = '<span style="color:coral">'+data1+' '+ flag+' '+ data2+' = '+temp +'</span>'

			<!-- var str = '<span style="color:coral">' -->
			<!-- str += data1+' '+flag+' '+data2 + ' = ' + temp  -->
			<!-- str += '</span>' -->
			<!-- jieguo.innerHTML = str -->
		}


	</script>
</body>
</html>

运行实例 »

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运算结果

计算器.jpg

总结

手写

Correction status：qualified

Teacher's comments：

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