<?php
$a= $_POST['number1'];
$b= $_POST['number2'];
$v= $_POST['s'];
if($v=="+"){
echo "结果为：".($a+$b);
}elseif($v=="-"){
echo "结果为：".($a-$b);
}elseif($v=="*"){
echo "结果为：".($a*$b);
}elseif($v=="/"){
if($a==0){
echo "除数不能是0";
}else{
echo "结果为：".($a/$b);
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>练习</title>
</head>
<body>
<form method="post" action="lx02.php">
<h2>作业二：</h2>
<input type="text" name="number1">
<select name="s">
<option >-请选择符号-</option>
<option value="+">加</option>
<option value="-">减</option>
<option value="*">乘</option>
<option value="/">除</option>
</select>
<input type="text" name="number2">
<input type="submit" name="js" value="计算">
</form>
</body>
</html>