PHP Form Validation Showing Errors Before Submission - php

Question

I am working on making a PHP and MySQL application for practicing my new-found love for programming. I have a login script; the HTML form is as follows:
<form action="<?php echo $_SERVER["PHP_SELF"]; ?>" method="post">
Username:
<input type="text" name="username" maxlength="60"><br />
Password:
<input type="password" name="password" maxlength="60"><br />
Confirm Password:
<input type="password" name="password_confirm" maxlength="60"><br />
<input type="submit" name="submit" value="Register"><br />
</form>
This continues into the PHP form validator:
<?php
$username_original = $_POST["username"];
$password_original = $_POST["password"];
$password_confirm_original = $_POST["password_confirm"];
//This makes sure they did not leave any fields blank
function FieldComplete($user, $password, $password_confirm) {
if (!isset($user, $password, $password_confirm) &&
$user && $password && $password_confirm == "" || " ") {
$field_confirm = false;
} else {
$field_confirm = true;
}
if ($field_confirm == true) {
echo "";
} else {
echo "You did not complete all the required fields.";
}
}
FieldComplete($username_original, $password_original, $password_confirm_original);
?>
I realize that making a function for this might seem a little useless, but it was as close as I got to the result I wanted.
However, this code displays the error "You did not complete all the required fields." on loading of the page. I only want that error to display if they have pressed the register button and still have a blank field.
Any advice or help is greatly appreciated. Thanks StackOverflow community!

Answer 1

If you want to run the php code only if button is submitted so you need to check about that at the top of your page
if(isset($_POST["submit"]))
{
//form has been submitted
//do validation and database operation and whatever you need
} else {
//form has not been submitted
//print the form
}

Answer 2

In addition to Fabio answer, you can improve your code like this:
if(isset($_POST['submit'])){
$username_original = $_POST["username"];
$password_original = $_POST["password"];
$password_confirm_original = $_POST["password_confirm"];
$isComplete = FieldComplete($username_original, $password_original, $password_confirm_original);
if(!$isComplete){
echo "You did not complete all the required fields.";
}
}else{
//display the form
}
function FieldComplete($user, $password, $password_confirm) {
if (!isset($user, $password, $password_confirm) &&
$user && $password && $password_confirm == "" || " ") {
return false;
} else {
return true;
}
}