PHP - 我想在单击type =“reset”按钮时将值设置为false。 我怎样才能做到这一点？

Question

I have been trying to learn PHP for the past week now.
I have created a form which acts like a calculator in which two values are either added up, subtracted, multiplied or divided.

$cal = new calculator();
if(isset($_POST['submit']))
{   
    $result = $cal->getresult($_POST['n1'],$_POST['n2'],$_POST['op']);
}

if(isset($_POST['reset'])){   
$result = false;
}

?>

<form method="post">
<table align="center">
    <tr>
        <td><b><?php echo $result; ?></b></td>
    </tr>
    <tr>
        <td>Zahl 1 </td>
        <td><input type="number" name="n1"></td>
    </tr>

    <tr>
        <td>Zahl 2 </td>
        <td><input type="number" name="n2"></td>
    </tr>

    <tr>
        <td>Select Oprator</td>
        <td><select name="op">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select></td>
    </tr>

    <tr>
        <td></td>
        <td><input type="submit" name="submit" value="Berechnen"></td>
    </tr>

    <tr>
        <td></td>
        <td><input type="reset" name="reset" value="Reset"></td>
    </tr>

</table>
</form> 

Beforehand I define the calculator-class but it is not relevant for this question.
So what I want to do is when I click the

<td><input type="reset" name="reset" value="Reset"></td>

button i want the variable $result to be defined as empty, which I want to achieve by

if(isset($_POST['reset'])){   
$result = false;
}

In effect, php should not show the result on top of the document, because

<tr>
        <td><b><?php echo $result; ?></b></td>
    </tr>

is empty?

Unfortunately, that doesn't happen. Does anyone know how to fix this?

Answer 1

The reset button won't submit your form, which is what needs to happen in order for your PHP to run. You can, however, use multiple submit buttons in a form and name them differently. Try this:

<input type="submit" name="reset" value="Reset">

This will trigger the form to submit, but will come across as "reset" in your POST data, and should subsequently trigger your logic to clear values.

---

EDIT:

The $result variable is dead once your page is processed server side. By time it shows up in your browser, that part of the request is over and the variable doesn't exist, so clicking a "reset" button doesn't really matter. It sounds like you want to clear the form and also clear the result display. In that case, continue to use the reset button as you were.

And then add some javascript to clear out the result. For that to work, you need to add an ID or class to the element holding it:

<tr>
    <td>
       <b id="result">
          <?php echo $result; ?>
       </b>
    </td>
</tr>

Then add a click handler, either in a JS file, in <script> tags, or right on the element itself:

<input type="reset" name="reset" value="Reset" onClick="document.getElementById('result').innerHTML='0';">

That would set it to "0".