HTML Form Validation in PHP. - php

Question

I am completely brand-new to php and after researching about it I am still unable to find the appropriate answer. As I am trying to get my form validated with php and the error messages customised with CSS.
My HTML code is :
<div class="container">
<form action="/action_page.php">
<div class="flex-row">
<input type="text" id="name" name="name" placeholder="Name">
<input type="email" id="email" name="email" placeholder="Email Address">
<input type="number" id="age" name="age" placeholder="Age">
</div>
<div class="flex-row">
<input type="text" id="subject" name="subject" placeholder="Subject">
<select type="dropdown" name="contact" placeholder="Age">
<option placeholder="australia">Australia</option>
<option value="canada">Canada</option>
<option value="usa">USA</option>
</select>
</div>
<div class="flex-row">
<textarea id="message" name="message" placeholder="Talk To Us" style="height:200px"></textarea>
</div>
<input type="submit" value="Submit">
</form>
My CSS is on pastebin below:
Pastebin
P.S I am also thinking about putting the for validation code into a separate file and that file will be saved into the includes folder.

Answer 1

The data will be available in the php-script through the $_GET global variable as an array. Each input is an item in this array, e.g. $_GET["name"].
The script action_page.php could look something like this (this is just a beginning...):
<?php
//Test the input, for example like this:
if(empty($_GET["name"])) $error="You need to provide a name";
if(strpos($_GET["email"],"#")==0) $error="The e-mail is not valid"; //Of course you could test for a lot more, for example using regular expressions
//Now you can build your response to the user
if($error) {
echo ("<h1>Error</h1>".$error);
}
include("form.html"); //If you want to show the same form again.
You could also include the errors more integrated in the form - but then you would need to integrate PHP into the HTML.
You will find good documentation at http://www.php.net, and http://w3schools.com/ has a lot of good stuff as well.