PHP MySQL if date and time unavailable add to alert message - php

Question

I am fairly new to PHP and a new student and so I will ask in advance to please forgive me if I have made errors that will be clearly obvious to someone experienced.
I am working on a page submission form that connects to a mysql database to either check for an existing value and if it does not exist then logs a string value of the datetime picker and also appends an id number to make a unique value to a table whenever someone was to press submit, and after form validation is accepted. Submitting if the record does not exist works and is ok.
However, whenever a record already exists, rather than displaying in the error message that the time is unavailable, the entire page just goes blank.
Initially, I had a button that would check to see if the record existed in the mysql table but I then decided it would be more efficient to try to include the date validation check of mysql table while completing the form validation and this is where I have trouble and of course the page breaks and nothing is displayed.
If someone could please guide me I would be most grateful.
it seems I am unable to add more code, but I will add what was wrong.
I did need to initialize $error=''; also $DateTime, and $id at the top of the script, I had it below but had forgotten to place it above and that was causing my problem.
<?php
$userid = "1";
$strid = strval($id);
$DateTimeCheck = $DateTime . $strid;
$con = new PDO("mysql:host=$host;dbname=$dbname", $user, $password);
$con->exec("SET CHARACTER SET utf8");
$sql = "SELECT booked FROM user_booking WHERE `booked` = :booked";
$sqlprep = $con->prepare($sql);
$ar_val = array(':booked' => $DateTimeCheck);
if (isset($_POST['datetime'])){
if (!$_POST['name']) {
$error = "<br/>- Please enter your name";
}
if (!$_POST['email']) {
$error .= "<br/>- Please enter your email";
}
if (!$_POST['message']) {
$error .= "<br/>- Please enter a message";
}
if (!$_POST['check']) {
$error .= "<br/>- Please confirm you are human";
}
if ($sqlprep->execute($ar_val)) {
while ($row = $sqlprep->fetch(PDO::FETCH_OBJ)) {
$DateTimeExists = $row->booked;
}
}
if (isset($DateTimeExists) && $DateTimeExists != ''){
$error .= "<br/>- The time you have requested is unavailable";
}
if ($error) {
$result = '<div class="alert alert-danger" role="alert"><strong>Whoops, there is an error</strong>. Please correct the following: ' . $error . '</div>';
} else {
mail("#gmail.com", "Contact message", "Name: " . $_POST['name'] . "
Email: " . $_POST['email'] . "
When: " . $_POST['datetime'] . "
Message: " . $_POST['message']);
{
$result = '<div class="alert alert-success" role="alert">Thank you, someone will be in touch soon to confirm your appointment. </div>';
$id = "$userid";
$strid = strval($id);
$DateTime = $_POST['datetime'];
$DateTimeCheck = $DateTime . $strid;
$strid = strval($id);
$con = new PDO("mysql:host=$host;dbname=$dbname", $user, $password);
$con->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$sql = "INSERT INTO user_booking ( user_id, booked ) VALUES ( :id, :booked )";
$q = $con->prepare($sql);
$q->execute(array(':booked' => $DateTime . $strid,
':id' => $id));
$con = null;
}
}
}
?>
Here is the markup for the form.
<form method="post" role="form">
<div class="form-group">
<input type="text" name="name" class="form-control" placeholder="Your name"
value="<?php echo $_POST['name']; ?>">
</div>
<div class="form-group">
<input type="email" name="email" class="form-control" placeholder="Your email"
value="<?php echo $_POST['email']; ?>">
</div>
<div class="form-group" align="left">
<label class="control-label">Date/Time</label>
<div class='input-group date' id='datetimepicker1'>
<input type='text' name="datetime" class="form-control" placeholder="desired time"
value="<?php echo $_POST['datetime']; ?>">
<span class="input-group-addon">
<span class="glyphicon glyphicon-calendar"></span>
</span>
</div>
</div>
<div class="form-group">
<textarea name="message" rows="5" class="form-control"
placeholder="message..."><?php echo $_POST['message']; ?></textarea>
</div>
<div class="checkbox" align="left">
<label class="readable" align="left">
<input type="checkbox" name="check"> I am human
</label>
</div>
<div align="left">
<input type="submit" name="submit" class="btn btn-success" value="Book Appointment!"/>
</div>
</form>

Answer 1

If you are using .= you need to first initialise the variable before .= will work on the variable.
You attempted to do that in this IF block
if (!$_POST['name']) {
$error = "<br/>- Please enter your name";
}
but if that error is not present you will never actually initialise the $error variable.
So the simple solution is to initialise $error before getting into this section of code
$error = '';
if (isset($_POST['datetime'])){
// So now you can change this test to use .=
if (!$_POST['name']) {
$error .= "<br/>- Please enter your name";
}
Now the variable will be testable later in the code
If this is in fact the problem here, you should have been getting errors reported. If you didnt see any then try adding these lines of code to any problem script while you test it
ini_set('display_errors', 1);
ini_set('log_errors',1);
error_reporting(E_ALL);
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);