PHP验证问题与/单独的无线电答案和粘性表格

Question

I am trying to create a quiz where the user is answering multiple questions.

I made each question using radios and i am trying to check if that radio is checked. if the radio is not check then i display an error. I mostly got that part working.
My issues is that say if questions 1 has a radio that is checked and question 2 was not answered, when the user hits submit then the answer they put for question 1 is gone.

I want to keep the answer that they checked, like a sticky form, and only display the error on the questions, in this case question 2, that they did not answer. Below is two different ways i tried to solve it and i cant seem to accomplish it.

This is how i am displaying the question with php.

<tr>
    <td> If a and b are negative numbers, and |a| < |b|, then b - a is negative. </td>
    <td> <?php echo ($err['q[1]']? "<span style='color:red'>*".$err['q[1]']."</span><br>": "");?>
        <input type="radio" name="q[1]" id="q[1]t" value="T"  <?php if (isset($_POST['q[1]']) and $_POST['q[1]'] == 'T') { echo 'checked'; } ?> > TRUE
        <input type="radio" name="q[1]" id="q[1]f" value="F"  <?php if (isset($_POST['q[1]']) and $_POST['q[1]'] == 'F') echo 'checked'; ?> > FALSE
    </td>
</tr>
<tr>
    <td> The equation 2x + 7 = 2(x + 5) has one solution. </td>
    <td>    <?php echo ($err['q[2]']? "<span style='color:red'>*".$err['q[2]']."</span><br>": "");?>
        <input type="radio" name="q[2]" id="q[2]t" value="T"  <?php if (isset($_POST['q[2]']) and $_POST['q[2]'] == 'T') echo 'checked'; ?> > TRUE
        <input type="radio" name="q[2]" id="q[2]f" value="F"  <?php if (isset($_POST['q[2]']) and $_POST['q[2]'] == 'F') echo 'checked'; ?> > FALSE
    </td>
</tr>

This is how i am trying to verify it.

if (isset($_POST) && !empty($_POST)) {

    if (isset($_POST['q[1]'])) {
        $radio_input = $_POST['q[1]'];
        echo $radio_input;
        $error=false;
    } else {
        $err['q[1]']= "Please Select An Answer";
        $error=true;
    }
    if (empty($_POST['q[2]'])) {
        $err['q[2]']= "Please Select An Answer";
        $error=true;
    } else {
        $error=false;
    }

Answer 1

When you submit a form with inputs using array notation [], they will come back as array in the $_POST. You would access your inputs using e.g. $_POST['q'][1].

Just remember that $err['q[1]'] !== $err['q'][1]

<?php
$err = array();
// check if form was submitted with POST
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    // simplified
    for ($i = 1; $i <= 2; $i++) {
        // check if no answer was selected
        if (empty($_POST['q'][$i])) {
            $err["q[$i]"] = "Please Select An Answer";
        }
    }
}
?>

<form action="" method="post">
    <table>
        <tr>
            <td> If a and b are negative numbers, and |a| < |b|, then b - a is negative.</td>
            <td> 
                <?php if (isset($err['q[1]'])) : ?>
                    <span style="color: red">* <?= $err['q[1]'] ?></span><br>
                <?php endif ?>
                <input type="radio" name="q[1]" id="q[1]t" value="T" <?= isset($_POST['q'][1]) && $_POST['q'][1] == 'T' ? 'checked' : '' ?>> TRUE
                <input type="radio" name="q[1]" id="q[1]f" value="F" <?= isset($_POST['q'][1]) && $_POST['q'][1] == 'F' ? 'checked' : '' ?>> FALSE
            </td>
        </tr>
        <tr>
            <td> The equation 2x + 7 = 2(x + 5) has one solution. </td>
            <td>    
                <?php if (isset($err['q[2]'])) : ?>
                    <span style="color: red">* <?= $err['q[2]'] ?></span><br>
                <?php endif ?>
                <input type="radio" name="q[2]" id="q[2]t" value="T" <?= isset($_POST['q'][2]) && $_POST['q'][2] == 'T' ? 'checked' : '' ?>> TRUE
                <input type="radio" name="q[2]" id="q[2]f" value="F" <?= isset($_POST['q'][2]) && $_POST['q'][2] == 'F' ? 'checked' : '' ?>> FALSE
            </td>
        </tr>
        <tr>
            <td></td>
            <td><input type="submit" value="Check"></td>
        </tr>
    </table>
</form>