PHP计算器

作业内容：
1、练习下这堂课学的 
2、计算机的if 改为 switch 
3、自己增加下判断，不让结果为0， 或者 判断 传值的时候 不要小于0

<?php
$num1 = "";
$num2 = "";
$opt = "";
$result = 0;
foreach($_GET as $k => $v){
    $$k = $v;
}
if($num2 == 0 and ($opt == 4 or $opt == 5)){
    echo "除数不能为0";
}else{
    $num1 = (int)$num1;
    $num2 = (int)$num2;
    switch ($opt) {
        case '1':
            $result = $num1 + $num2;
            break;
        case '2':
            $result = $num1 - $num2;
            break;
        case '3':
            $result = $num1 * $num2;
            break;
        case '4':
            $result = $num1 / $num2;
            break;
        case '5':
            $result = $num1 % $num2;
            break;
        default:
            break;
    }
}
?>
<!DOCTYPE html>
<html lang="zh_CH">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>PHP计算器</title>
    <style>
        *{
            margin: 5px;
            padding: 5px;
            font-size: 20px;
            height: 36px;
        }
        .input{
            width: 100px;
        }
        .input2{
            width: 100px;
        }
        select{
            width: 50px;
        }
    </style>
</head>
<body>
    <form action="" method="GET">
        <input class="input" type="number" name="num1" value="<?=$num1; ?>">
        <select name="opt">
            <?php
            $opts = ['+', '-', '*', '/', '%'];
            $html = "";
            foreach($opts as $k => $v){
                if(isset($_GET['opt']) && $_GET['opt'] == $k+1){
                    $html .= '<option value="'.($k+1).'" selected>'.$v.'</option>';
                }else{
                    $html .= '<option value="'.($k+1).'">'.$v.'</option>';
                }
            }
            echo($html);
            ?>
        </select>
        <input class="input" type="number" name="num2" value="<?=$num2;?>">
        <label class="input"><?=($result != "")?"= ".$result:""?></label>
        <!-- <br> -->
        <input class="input2" type="submit" value="计算">
        <input class="input2" type="button" value="重置" onclick="location.href='<?=$_SERVER['PHP_SELF'];?>'">
    </form>
</body>
</html>

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