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<?php$num1 = $_GET['num1'];$num2 = $_GET['num2'];$opt = $_GET['opt'];$result = 0;if(!is_numeric($num1)){$result = '请输入数字1';}else if(!is_numeric($num2)){$result = '请输入数字2';}else{switch($opt){case '+':$result = $num1 + $num2;break;case '-':$result = $num1 - $num2;break;case '*':$result = $num1 * $num2;break;case '/':if($num2 == '0'){$result = '除数不能为0 ！';}else{$result = $num1 / $num2;}break;case '%':if($num2 == '0'){$result = '除数不能为0 ！';}else{$result = $num1 % $num2;}break;default:$result = '无效运算！';};}?><!DOCTYPE html><html lang="en"><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>Document</title></head><body><form action="" method="get" style="width:20em;display:grid;grid-template-columns:30% 70%;gap:1em;"><label>数字1：</label><input type="number" name="num1" value="<?= isset($_GET['num1'])?$num1 :'' ?>"><label>运算符:</label><select name="opt" id=""><option value="+" <?= ($opt == '+') ? 'selected':'' ?> >+</option><option value="-" <?= ($opt == '-') ? 'selected':'' ?> >-</option><option value="*" <?= ($opt == '*') ? 'selected':'' ?> >*</option><option value="/" <?= ($opt == '/') ? 'selected':'' ?> >/</option><option value="%" <?= ($opt == '%') ? 'selected':'' ?> >%</option></select><label>数字2：</label><input type="number" name="num2" value="<?= isset($_GET['num2']) ?$num2 : '' ?>"><label>结 果：</label><input type="text" value = "<?= $result ?>"><label></label><input type="submit" value="提交"></form></body></html>
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