Pass value from form to alter file PHP without POST - php

Question

I´m trying to pass ALTER a value from my database with a form.
Because of the POST action, I putted the n_processo (primarykey) on the form so the POST can pass it to the file and edit the table.
I don´t want this value to appear on the table (Form), because it´s readonly, so that the POST can see it and edit the values.
Does anyone know how to change that?
Form file:
<form action="alterar_aluno3.php" method="POST">
<table>
<tr>
<th width="15%">Nº de Aluno</th>
<td><input type="text" maxlength="5" class="input-field4" name="teste" readonly value="<?php echo $idaluno;?>"/></td>
</tr>
<tr>
<th width="20%">Pessoas com quem vive:</td>
<td><input type="text" class="input-field4" name="agregado_existente" value="<?php echo $agregado_existente;?>"/></td>
</tr>
</table>
<p align=right>
<!--alterar este botao -->
<button type="submit" value="Alterar">Alterar</button>
<button type="cancel" onclick="window.location='http://donutsrool.pt/ficha_aluno.php';return false;">Cancelar</button>
</p>
</form>
Insert file:
<?php
include "functions.php";
session_start();
//captar os dados recebidos do formulário com o método POST
$idaluno1=$_POST['teste'];
$agregado_existente = $_POST['agregado_existente'];
$altera="UPDATE aluno SET `agregado_existente`='$agregado_existente' WHERE `n_processo`=$idaluno1;";
$resultado =DBExecute($altera);
header("Location: ficha_aluno.php");
?>

Answer 1

You can put id in a hidden field instead of text field.
<input type="hidden" maxlength="5" class="input-field4" name="teste" value="<?php echo $idaluno;?>"/>
Hidden fields work the same as of text fields.
Their value can only be set with PHP on page load or through JavaScript events.
Only difference is that they are not visible on browser.
Though, they can be seen in View Source of the page.

Answer 2

Try this:
<?php
include "functions.php";
session_start();
//captar os dados recebidos do formulário com o método POST
$idaluno1=$_POST['teste'];
$agregado_existente = $_POST['agregado_existente'];
$altera="UPDATE aluno SET `agregado_existente`='$agregado_existente' WHERE `n_processo`='$idaluno1'";
$resultado =DBExecute($altera);
header("Location: ficha_aluno.php");
?>