I'm trying to get my code to display an error message when username field and password field are not filled. It doesn't work when i use If(isset) but when i use if (normal code) it seems to work. Any help will be appreciate it.

Here is the code : 

Login.php

```
<?php

if (isset($_POST['log_username']) && isset($_POST['log_password'])){

    $log_uname = preg_replace('#[^A-za-z0-9]', '', $_POST["log_username"]);
    $log_password = preg_replace('#[^A-za-z0-9]#i', '', $_POST["log_password"]);

    //get user from database
    $sql = mysql_query("SELECT * FROM users WHERE username='$log_uname' AND password='$log_password' LIMIT 1");

    //check user existance
    $userCount = mysql_num_rows($sql);

    if ($userCount == 1) {

        while($row = mysql_fetch_array($sql)){

            $id = $row["id"];

        }
        $_SESSION['id'] = $id;
        $_SESSION['log_username'] = $log_uname;
        $_SESSION['log_password'] = $log_password;

    }else{

        die (msg1(0, "Information Incorrect"));

    }

}

function msg1($status1,$txt1){

    return '{"status1":'.$status1.',"txt1":"'.$txt1.'"}';

}
?>

```

login.js

```
$(document).ready(function (){

    $('.login_form').submit(function(e) {

        login();
        e.preventDefault();

    });

    function login(){
    hideshow1('loading1',1);
    error1(0);

    $.ajax({

        type: "POST",
        url: "php/login.php",
        data: $('.login_form').serialize(),
        dataType: "json",
        success: function(msg1){
            if(parseInt(msg1.status1)==1){
                window.location=msg1.txt1;
            }
            else if (parseInt(msg1.status1)==0){

                error1(1,msg1.txt1);

            }
            hideshow1('loading1',0)
        }

    });
    }

    function hideshow1(el,act){
        if(act) $('#'+el).css('visibility','visible');
        else $('#'+el).css('visibility','hidden');
    }
    function error1(act,txt1){
        hideshow1('error1',act);
        if(txt1) $('#error1').html(txt1);
    }

});

```

and last Index.php

```
   <?php include ("php/head.php");?>
<div id="wrapper">

    <div id="container">

        <div id="intro">

            <h2><center>Are you a member? Login ...</center></h2>
            <h3><center>And enjoy hundreds of services.</center></h3>

            <div id="log_form">

                <form action="php/login.php" method="POST" class="login_form">

                    <input type="text" size="25" name="log_username" id="login_txt" placeholder="Your Username">
                    <input type="password" size="25" name="log_password" id="login_pass" placeholder="Your Password">
                    <label id="check"><input type="checkbox" name="checkbox"> Remember Me</label>
                    <input type="submit" name="submit1" id="login_sub" value="LogIn">
                    <img id="loading1" src="images/ajax-loader.gif" alt="working.." />

                <script>

                $("#login_txt,#login_pass").click(function (e) {

                    e.preventDefault();

                    $('#error1').fadeOut('fast', function () {

                            $(this).show();
                            $(this).css("visibility","hidden");             
                    });

                });

                </script>

                </form>

                <div id="error1"></div>

            </div>

            <div id="new_users">

                <h4 class="h4_users">New Users ...</h4>

                <a href="#"><img src="#" width="55" height="55"></a>
                <a href="#"><img src="#" width="55" height="55"></a>
                <a href="#"><img src="#" width="55" height="55"></a>
                <a href="#"><img src="#" width="55" height="55"></a>

            </div>

        </div>

        <div id="register">

            <h2><center>Sign up Below ...</center></h2>
            <h3><center>Easy, fast and free!</center></h3>

                <form action="php/register.php" method="POST" name="form" class="form">
                   <input type="text" size="25" name="fname" placeholder="First Name" id="fname" >
                   <input type="text" size="25" name="lname" placeholder="Last Name">
                   <input type="text" size="25" name="username" placeholder="Username">
                   <input type="text" size="25" name="email" placeholder="Email">
                   <input type="text" size="25" name="email2" placeholder="Repeat Email">
                   <input type="password" size="25" name="password" placeholder="Password">
                   <input type="password" size="25" name="password2" placeholder="Repeat Password">
                   <input type="submit" name="submit" id="sub" value="Sign Up!">
                   <img id="loading" src="images/ajax-loader.gif" alt="working.." />
                </form>

                <script>

                $('#fname').click(function (e) {

                    e.preventDefault();

                    $('#error').fadeOut('fast', function () {

                            $(this).show();
                            $(this).css("visibility","hidden");             
                    });

                });

                </script>

            <div id="error"></div>

        </div>

    </div>

    <?php include("php/footer.php");?>

</div>
</body>
</html>

```