preventing altered input value checkbox - php

Question

I have a form with multiple checkboxes that can be selected. If a user wanted they could go in and change the value in the checkbox. I want to know if there is a way I can not accept the form or display an error if the value submitted was not one of the original choices displayed. Here is my code:
HTML Code:
<form action="" method="post">
<table>
<tr>
<td>
<input type="checkbox" name="checkbox[]" value="1">
</td>
<td>
<input type="checkbox" name="checkbox[]" value="2">
</td>
<td>
<input type="checkbox" name="checkbox[]" value="3">
</td>
<td>
<input type="checkbox" name="checkbox[]" value="4">
</td>
<td>
<input type="checkbox" name="checkbox[]" value="5">
</td>
<td>
<input type="checkbox" name="checkbox[]" value="6">
</td>
</tr>
</table>
<input type="submit" name="submit" value="submit">
</form>
PHP Code:
<?php
if(!empty($_POST['checkbox'])) {
foreach($_POST['checkbox'] as $check) {
echo $check;
}
}

Answer 1

If you want, since html is static (which I dont know why), you could initialize some original values, then compare it. Consider this example:
<?php
$original_values = array(1, 2, 3, 4, 5, 6);
if(isset($_POST['submit'], $_POST['checkbox'])) {
$submitted_values = $_POST['checkbox'];
foreach($submitted_values as $value) {
if(!in_array($value, $original_values)) {
// this particular submitted value does not belong to the original values that is set
echo 'not good';
exit;
}
}
// all good if it goes down here
echo 'all good';
}
?>
<form method="POST" action="">
<table border="0" cellpadding="10">
<tr>
<?php foreach($original_values as $value): ?>
<td><input type="checkbox" name="checkbox[]" value="<?php echo $value; ?>" /></td>
<?php endforeach; ?>
</tr>
<tr><td colspan="6"><input type="submit" name="submit" value="submit" /></td></tr>
</table>
</form>
Note: To test, try to change the values thru the browser [most likely F12], change the dom values. Example: Try to change a checkbox value attribute to 7 or 100, check it the submit.
Also another way:
$original_values = array(1, 2, 3, 4, 5, 6);
if(isset($_POST['submit'], $_POST['checkbox'])) {
$submitted_values = $_POST['checkbox'];
$differences = array_diff($submitted_values, $original_values);
if(count($differences) > 0) {
echo 'not good';
exit;
}
// all good if it goes down here
echo 'all good';
}
Print all the values inside a table:
if(isset($_POST['submit'], $_POST['checkbox'])) {
$submitted_values = $_POST['checkbox'];
$count = count($submitted_values);
echo "<table border='1' cellpadding='10'>";
echo "<tr><td colspan='$count'>Values</td></tr>";
echo "<tr>";
foreach($submitted_values as $value) {
echo "<td>$value</td>";
}
echo "</tr>";
echo "</table>";
}

Answer 2

Store values in a separate PHP file, checkbox_values.php:
<?php
$checkbox_values = array(1, 2, 3, 4, 5, 6);
?>
And your form, another PHP file, main.php:
<?php
require 'checkbox_values.php';
?>
<form method="POST" action="checkbox_process.php">
<table border="0" cellpadding="10">
<tr>
<?php foreach ( $checkbox_values as $check ) { ?>
<td><input type="checkbox" name="checkbox[]" value="<?php echo $check; ?>" /></td>
<?php } ?>
</tr>
<tr><td colspan="6"><input type="submit" name="submit" value="submit" /></td></tr>
</table>
</form>
And checkbox_process.php:
<?php
require 'checkbox_values.php';
if(!empty($_POST['checkbox'])) {
foreach($_POST['checkbox'] as $check) {
if ( in_array($check, $checkbox_values) ) { echo $check; }
}
}
?>