如何基于php / javascript中的用户输入生成动态文本框？

Question

This code below is displaying data through a dropdown and I was wondering on how can I convert this into like a when a user enters a number in a textbox and click set, dynamic dropdowns appear based on the number he entered.

$query = mysqli_query($con, "SELECT * FROM topic WHERE SubCat = $subcat ");
echo "<select name='topdd' >";
echo " <option>--None Selected--</option>";
while ($row = mysqli_fetch_array($query)) {
    echo "<option value='$row[topic_id]' selected>";
    echo $row["title"];
    echo "</option>";
}
echo "</select>";

Answer 1

This code it's ok for you ? I make your job, the next time try yourself

<form method="POST">
    <label for='choiceNumber'>Number of dropdowns choice</label>
    <input type='number' name='choiceNumber'>
    <input type='submit'>
</form>

<?php
    $resultArray = array(1,2,3,4,5,6,7);

    $display = "<select name='topdd'><option>--None Selected--</option>";
    if (!empty($_POST['choiceNumber']) && $_POST['choiceNumber'] > 0) {
        for($i = 0; $i < $_POST['choiceNumber']; $i++) {
            $display .= "<option>".$resultArray[$i]."</option>";
        }
    }
    echo $display."</select>";
?>