<!DOCTYPE html>
<html>
<head>
<title>PHP实现简单计算器（使用分支结构）</title>
</head>
<body>
<?php
$mess = "";
if(isset($_POST["sub"])) {
$mess .="第一个数不能为空！<br/>";
}else {
if(!is_numeric($_POST["num1"])){
$mess .="第一个数必须是数字！<br/>";
}
}
if($_POST["num2"] ==""){
$mess .= "第二个数不能为空！<br/>"
} else{
if(!is_numeric($_POST["num2"])){
$mess .="第二个数必须是数字！<br/>";
} else{ //第20行
if($_POST["opt"] == "/" && $_POST["num2"] == 0){
$mess .= "除数不能为0";
}
}
}
}
?>
<table style="border:1px; align:center; width:400px;">
<form action="" method="post">
<caption><h1>计算器</h1></caption>
<tr>
<td>
<input type="text" size="4" name="num1" value="<?php echo $_POST['num1'] ?>" />
</td>
<td>
<select name="opt">
<option value="+" <?php echo $_POST["opt"]=="+" ? "selected" : "" ?>> + </option>
<option value="-" <?php echo $_POST["opt"]=="-" ? "selected" : "" ?>> - </option>
<option value="*" <?php echo $_POST["opt"]=="*" ? "selected" : "" ?>> * </option>
<option value="/" <?php echo $_POST["opt"]=="/" ? "selected" : "" ?>> / </option>
<option value="%" <?php echo $_POST["opt"]=="%" ? "selected" : "" ?>> % </option>
</select>
</td>
<td>
<input type="text" size="4" name="num2" value="<?php echo $_POST["num2"] ?>"/>
</td>
<td>
<input type="sumbmit" name="sub" value="计算"/>
</td>
</tr>
</form>
<?php
if(isset($_POST["sub"])){
echo '<tr><td colspan="4">';
if(!$mess){
$sum = 0;
switch($_POST["opt"]){
case "+":
$sum = $_POST["num1"] + $_POST["num2"];
break;
case "-":
$sum = $_POST["num1"] - $_POST["num2"];
break;
case "*":
$sum = $_POST["num1"] * $_POST["num2"];
break;
case "/":
$sum = $_POST["num1"] / $_POST["num2"];
break;
case "%":
$sum = $_POST["num1"] % $_POST["num2"];
break;
}
echo "结果：{$_POST['num1']} {$_POST['opt']} {$_POST['num2']} = {$sum}";
}else{
echo $mess;
}
echo '</td></tr>';
}
?>
</table>
</body>
</html>
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