keep user input in fields after unsuccessful form submission

I have a validation function that checks user input. If the validation fails, unfortunately all the info they inputted disappears and they have to input everything again. This would annoy pretty much every user ever.

I tried something like this just to test out whether or not it would display the already inputted data. It works but it isn't very elegant. Is there  a better way? (This is just a test so there is no sanitizing etc.)

if(!isset($_POST['email'])) {
	$email = "";	
} else {
	$email = $_POST['email'];
}

<input type="text" name="email" class="form-control" value="<?php echo $email ?>">

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Black SulfurAsked:
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Ray PaseurConnect With a Mentor Commented:
Here is the design pattern.
https://iconoun.com/demo/form_highlight_errors.php
<?php // demo/form_highlight_errors.php
/**
 * Demonstrate how to highlight errors in form input, and remember valid inputs
 * Client is asked to put in a value
 * If the value fails our test we show an error message
 * We put a marker next to the input control on the form
 * We turn the form border red
 * SEE http://www.w3schools.com/CSS/pr_class_visibility.asp
 */
error_reporting(E_ALL);


// THESE STYLE ELEMENTS ARE SET FOR THE SCRIPT INITIALIZATION
$error_abc = $error_xyz = $error_any = 'hidden';
$boxer_abc = $boxer_xyz              = 'black';


// CAPTURE AND NORMALIZE THE POST VARIABLES - ADD YOUR OWN SANITY CHECKS HERE
$abc = (isset($_POST["abc"])) ? trim(strtoupper($_POST["abc"])) : NULL;
$xyz = (isset($_POST["xyz"])) ? trim(strtoupper($_POST["xyz"])) : NULL;


// IF ANYTHING WAS POSTED, VALIDATE IT
if (!empty($_POST))
{
    // VALIDATE THE 'abc' FIELD
    if ($abc != 'ABC')
    {
        // VALIDATION FAILED
        $error_abc = $error_any = 'visible';
        $boxer_abc = 'red';

        // BECAUSE THIS FAILED VALIDATION, REMOVE IT FROM THE FORM
        $abc       = NULL;
    }

    // VALIDATE THE 'xyz' FIELD
    if ($xyz != 'XYZ')
    {
        // VALIDATION FAILED
        $error_xyz = $error_any = 'visible';
        $boxer_xyz = 'red';

        // BECAUSE THIS FAILED VALIDATION, REMOVE IT FROM THE FORM
        $xyz       = NULL;
    }

    // DO WE HAVE INPUT FREE FROM ANY ERRORS?
    if ($error_any != 'visible')
    {
        echo "CONGRATULATIONS";
        die();
    }

    // OTHERWISE... OOPS - WE HAVE ERRORS AND MUST SHOW THE FORM AGAIN
}

// IF NOTHING WAS POSTED, OR IF THERE ARE ERRORS, WE NEED NEW CLIENT INPUT
$form = <<<ENDFORM
<style type="text/css" media="all">
.error_any { visibility:$error_any; }
.error_abc { visibility:$error_abc; }
.error_xyz { visibility:$error_xyz; }
</style>
<pre>
<form method="post">
<span class="error_any">PLEASE CORRECT THE FOLLOWING ERRORS</span>
<span class="error_abc">YOU MUST ENTER 'abc' IN THIS FIELD</span>
PLEASE ENTER "ABC" HERE: <input style="border-color:$boxer_abc;" name="abc" value="$abc" />
<span class="error_xyz">YOU MUST ENTER 'xyz' IN THIS FIELD</span>
PLEASE ENTER "XYZ" HERE: <input style="border-color:$boxer_xyz;" name="xyz" value="$xyz" />
<input type="submit" />
</form>
ENDFORM;

// WRITE THE FORM WITH THE APPROPRIATE CSS STYLES ON THE ERROR MESSAGE FIELDS
echo $form;

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Black SulfurAuthor Commented:
Awesome, thanks!
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