PHP:my session_variables shows when the page refresh - php

Question

I know this is very simple thing but i am not aware of this. I have php code on same page for a signup form which have some session variables to be shown when any condition matches with the code.
The code structure is like this:
<?php
session_start();
if(isset($_POST['signup'])
{
if(condition)
{
$_SESSION['err1']="string";
}
else
{
$_SESSION['err2']="string";
}
}
?>
//HTML form
<?php if(isset($_SESSION['err1']) {?>
<li><?php echo $_SESSION['err1'];}?></li>
<?php if(isset($_SESSION['err2']) {?>
<li><?php echo $_SESSION['err2'];}?></li>
//rest of the form
I have more block of if-else in my code. Initially, when an condition is matched, the session message is shown. But as soon as the page refresh an another session message is shown along with previous session message.
Is this correct way of coding with forms? Because i want to show error messages inside the html form.

Answer 1

That's maybe because you do not empty your session variable.
Between 2 HTTP request, the session is kept on the server (juste reloading at each request).
So, if you are putting a message on $_SESSION['error1'] for the first call, it will show it. Then, on the second load, if you are putting a message on $_SESSION['error2'], you will also have the message of error1 because the session keep your data.
After showing the form, you should empty all your session messages

Answer 2

Simply unset your session variable after you echo.
<li><?php echo $_SESSION['err1'];} unset($_SESSION['err1']); ?></li>

Answer 3

This is really a bad example that use session to echo errors.
what i do many times at the starting of my php.
$errors = array(); // make a empty array errors before the conditional statements
if ($_SERVER['REQUEST_METHOD'] == 'POST' && isset($_POST['Submit'])) {
//handle your POST variable
if(condition1){
$errors[] = "some error";
}
if(condition2) {
$errors[] = "some another error";
}
//more conditions
if (!empty($errors)) {
//process your form data if there is no errro
} else {
//display back your form along with Errors
if(isset($errors) && !empty($errors)) {
foreach($errors as $error) {
echo "<p class = 'error'>" . $error . "</p>";
}
}
<form action = "" method = "POST">
//your form elements
</form>
}
}

Answer 4

in first line of the php page, u can write
you can try any of the three lines between if condition
if(isset($_SESSION))
{
unset($_SESSION);
unregister($_SESSION['variable-name']) // try this also
session_destroy(); //try this also
}