How to set checkboxes to checked in loop? - php

Question

I wonder how I can make sure a checkbox is checked on a postback if for example someone leaves the addressfield blank it should then make sure the user doesn't have to refill the whole form again. In this case I'm generating 31 checkboxes. It's really frustrating.
$output_checkbox = '';
$checked = '';
for ($i=1; $i <= 31; $i++) {
if (isset($_POST['dagen'])) {
foreach ($_POST['dagen'] as $dag) {
if ($dag == $i) {
$checked . $i = 'checked';
}
}
}
$output_checkbox .= '<input type="checkbox" name="dagen[]" value="' . $i . '" id="day_' . $i . '"' . $checked . ' /><label for="day_' . $i . '">Dag ' . $i . '</label>';
}
Here is the form but there isn't the problem:
<form action="<?php echo $_SERVER['REQUEST_URI']; ?>" method="post">
<div>
<label for="email">Email:</label>
<input id="email" type="text" name="email" value="<?php if(isset($_POST['email'])) { echo $_POST['email'];} ?>" />
</div>
<div>
<label for="month">Maand:</label>
<select id="month" name="month">
<?php echo $output; ?>
</select>
</div>
<div>
Dagen:
<?php echo $output_checkbox; ?>
</div>
<input type="submit" name="btnSend" value="Verzenden" />
</form>
Here is an example of how I normally do it but it's a lot easier since it comes out of a database:
$output = '';
while ($row = $result->fetch_array(MYSQLI_BOTH)) {
$selected = '';
if (isset($_POST['month']) && $_POST['month'] == $row['id']) {
$selected = 'selected';
}
$output .= '<option value="' . $row['id'] . '"' . $selected . '>' . $row['naam'] . '</option>';
}

Answer 1

Something like this:
$output_checkbox = '';
for ($i=1; $i <= 31; $i++) {
if (isset($_POST['dagen'])) {
foreach ($_POST['dagen'] as $dag) {
if ($dag == $i) {
$checked = 'checked';
}
else{
$checked = '';
}
$output_checkbox .= '<input type="checkbox" name="dagen[]" value="' . $i . '" id="day_' . $i . '"' . $checked . ' /><label for="day_' . $i . '">Dag ' . $i . '</label>';
}
}
}