Untitled

<?php

// In one place, set a variable that is readable to use anywhere
// you need to know this. It is cleaner code later, and better readable

$bIsPosted = ( count( $_POST ) > 0 );

// Set a variable to contain any errors, and one to say if there were no errors (default to true)
$aErrors   = [];
$bNoErrors = true;

// Initialize variables that will display in the form. Do this so they DO exist before form
// is submitted, and you can set defaults to display in form (ie. default the country)

$name    = '';
$email   = '';
$country = 'US';

if ( $bIsPosted ) {

    // This whole block only gets done if the form was submitted
    // For simplicity here, assuming it was a proper form, with all needed
    // inputs included

    $name  = trim( $_POST['name'] );
    $email = trim( $_POST['email'] );
    // and your others....

    // Validate Values FOR SIMPLICITY, Make sure all error messages are using needed
    // HTML entities ready to display
    if ( $name == '' ) {
        $aErrors[] = 'Name is required';
    }

    if ( $email == '' ) {
        $aErrors[] = 'Email is required';
    } elseif ( ! filter_var( $email, FILTER_VALIDATE_EMAIL ) ) {
        $aErrors[] = 'Email address is not valid';
    }

    // and other validation as needed.

    // Set the variable to say if there are errors
    $bNoErrors = ( count( $aErrors ) == 0 );

}

if ( $bIsPosted && $bNoErrors ) {

    // Code to build email and send it

} else {

    // Setup values for things such as select inputs in the form
    // Done here as they are not needed if the email was sent...

    $aCountries = [
        'US' => 'United States',
        'CA' => 'Canada',
        /* ... Others.... */
    ];

}

// At this point, all processing is done, now we output to the visitor,
// here are some functions to make the output code cleaner.

// This is a alias function to make output code cleaner later....
function hsc( $s ) {
    return htmlspecialchars( $s, ENT_QUOTES );
}

function outputOptions( $options, $default ) {
    foreach ( $options as $key => $val ) {
        if ( $key == $default ) {
            echo '<option value="', $key, '" selected="selected">', hsc( $val ), '</option>';
        } else {
            echo '<option value="', $key, '">', hsc( $val ), '</option>';
        }
    }
}

?>
<html>

<!-- all code up to the form area.... -->

<?php if ( $bIsPosted && $bNoErrors ) { ?>

    <div class="success">
        Your form was submitted sucessfully!
    </div>

<?php } else {  // Not submitted or has errors?>

    <?php if ( ! $bNoErrors ) { // There WERE errors ?>
        <div class="errors">
            Please check the following and try again:
            <ul>
                <li><?= implode( '</li><li>', $aErrors ); ?></li>
            </ul>
        </div>
    <?php } // end display errors ?>

    <form action="" method="post">
        <!-- kept basic here, need to add labels and formatting -->

        <input type="text" name="name" value="<?= hsc( $name ) ?>">

        <input type="email" name="email" value="<?= hsc( $email ) ?>">

        <select name="country">
            <?php outputOptions( $aCountries, $country ); ?>
        </select>

        <input type="submit" name="submit" value="Send Message">

    </form>
<?php } // end else posted and no errors ?>

<!-- all code after the form area.... -->

</html>