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How to make a form style hidden if a specific session is set? I did it that way

<form action="" method="post" <?php if ((isset($_SESSION['start']) )|| (isset($_SESSION['visitor']) )){ echo 'style="display:none;"'; } ?>>
    <input type="radio" name="log" id="viso" value="vis" checked onclick="javascript:yesnoCheck();"> Visitor<br> 
    <input type="radio" name="log" id="uso" value="use" onclick="javascript:yesnoCheck();" > User<br> 
    <label name="frm" id="frm" style="display:none" ><b>Password</b></label>
    <input type="password" style="display:none" name="pw" id="pw" placeholder="Enter Password" >
    <input type="submit" >
</form>
<?php
    if ( isset ($_POST['log'])&& $_POST['log']=="vis" )
    {
        $_SESSION["visitor"]="true";
        unset($_SESSION["start"]);
    }
    else if ( isset ($_POST['log'])&& $_POST['log']=="use" )
    {
        if ( isset($_POST['pw']) && $_POST['pw']!="1111" )
            echo "Wrong password";
        else if ( isset ($_POST['pw'])&& $_POST['pw']=="1111" )
        {
            $_SESSION['start']="Welcome";
            unset($_SESSION["visitor"]);
        }
    }
?>

but it's only hidden if i press on the submit button twice not from the first time

You have a simple logical flaw .You are checking for session before you set them .When user fills form and submits , your php runs this

 <form action="" method="post" id="lol" <?php if ((isset($_SESSION['start']) )|| (isset($_SESSION['visitor']) )){ echo 'style="display:none;"'; } ?>>

Note that at this time no session is set so form will not have display:noneand will get displayed **even though user has entered his details correctly still when response come form will be visible.Now to fix the issue move your session check before form display code

<?php
if ( isset ($_POST['log'])&& $_POST['log']=="vis" )
{
    $_SESSION["visitor"]="true";
//....more stuff 

 //...
 } ?>

 <form action="" method="post" id="lol" <?php if ((isset($_SESSION['start']) )|| (isset($_SESSION['visitor']) )){ echo 'style="display:none;"'; } ?>>