Appending value to variable - php

Question

Hoping someone can steer me in the right direction. I have a form with an input field and a button. When the input field is populated and the button clicked the value of the field displays in the variable $capture_numbers.
Id like to be able to add to that value i.e person enters 1, $capture_numbers displays 1, person enters 2, $capture_numbers now displays 1, 2, person enters 3, $capture_numbers now displays 1, 2, 3 and so on. I'm thinking along the lines of storing the previous value and appending to it but cant figure out how it's done. Below is my script.
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>">
<fieldset>
<input type="text" name="mynumbers[]">
<button>add another numbers</button>
<input type="submit" value="Submit" title="submit">
</fieldset>
</form>
<?php
if(isset($_POST['mynumbers']) && is_array($_POST["mynumbers"])) {
$capture_numbers = ' ';
foreach($_POST["mynumbers"] as $key => $value) {
$capture_numbers .= $value .", ";
}
echo $capture_numbers;
}
?>

Answer 1

You will need some persistent storage to store previous submissions. Valid options are a database, local storage, cookies, session etc.
In this example, I used session. When the form is submitted, check the session for previous entries and then append the new one to the list. I've added comments in the code.
Edit: You don't need to add the text field as an array. Ie. name="mynumbers[]". That is usually used for when you have multiple inputs with the same name and want to read them as an array.
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>">
<fieldset>
<input type="text" name="number">
<button>add another numbers</button>
<input type="submit" value="Submit" title="submit">
</fieldset>
</form>
<?php
// Start the session
session_start();
// Check if form is submitted
if (!empty($_POST)) {
// Create a variable to store all numbers
$allNumbers = [];
// Does the session contain anything
if (isset($_SESSION['previous'])) {
// Grab it from the session as an array and store it
$allNumbers = explode(',', $_SESSION['previous']);
}
// Append the new number to the list
$allNumbers[] = $_POST['number'];
// Convert it to a comma separated string
$capture_numbers = implode(',', $allNumbers);
// Store the entire list in the session
$_SESSION['previous'] = $capture_numbers;
// Output the result
echo $capture_numbers;
}