How to use session uniquely each time page loads?

[phpchild]

i want to use unique session values, set according to if condition. To use in same page.
Like this

<?php
 
session_start();
?> <form action="http://bytes.com/nn.php" method="post">
Username: <input type="text" name="lname"  /><br><br>
Password: <input type="password" name="password" /><br><br> <input type="submit" name="submit"/> </form> <?php if(isset($_POST['submit']) && $_POST['submit'])
{
echo "ok";
$_SESSION['a']="same";
 
}
echo $_SESSION['a'];
 
 
 
?>

But each time i load the page, i get the same session values even before i click submit button..
Any Help greatly appreciated.. Thanks in advances

[Exequiel]

if($_SESSION['user']=='' && $_SESSION['pwd']==''){
     echo 'Stay here.';
}else{
     echo 'Success';
}
 

Try this. . .