Forms allowing Blank entries

Hey i just started to learn php and i have a new user form and its allowing blank username , pass, and email help please

	if (isset($_POST['submit'])) { // Form has been submitted.
		$errors = array();

		// perform validations on the form data
		$required_fields = array('username', 'password','email');
		$errors = array_merge($errors, check_required_fields($required_fields, $_POST));

		$fields_with_lengths = array('username' => 30, 'password' => 30,'email' =>30);
		$errors = array_merge($errors, check_max_field_lengths($fields_with_lengths, $_POST));

		$username = trim(mysql_prep($_POST['username']));
		$password = trim(mysql_prep($_POST['password']));
		$hashed_password = sha1($password);
		$email    = trim (mysql_prep($_POST['email']));
		
		if ( empty($errors) ) {
			$query = "INSERT INTO ausers (
							username, hashed_password ,email
						) VALUES (
							'{$username}', '{$hashed_password}', '{$email}'
						)";
			$result = mysql_query($query, $connection);
			if ($result) {
				$message = "Welcome To JobLance $username" ;
			} else {
				$message = "The user could not be created.";
				$message .= "<br />" . mysql_error();
			}
		} else {
			if (count($errors) == 1) {
				$message = "There was 1 error in the form.";
			} else {
				$message = "There were " . count($errors) . " errors in the form.";
			}
		}
	} else { // Form has not been submitted.
		$username = "";
		$password = "";
		$email    = "";
	}
?>
			<h2>Create New User</h2>
			<?php if (!empty($message)) {echo "<p class=\"message\">" . $message . "</p>";} ?>
			<?php if (!empty($errors)) { display_errors($errors); } ?>
			<form action="myfirst.php" method="post">

PHP:

 

Add this:

if (empty($username))
{
    $errors[] = 'Enter a username';
}

PHP:

... right above this line:

if ( empty($errors) ) {

PHP:

 

Thanks Nico Quick Fix sorry im new to this