Cum pot afisa eroarea cand utilizatorul a scris un username gresit sau o parola gresita?

<?php
session_start();
include '_database.php';
$alertShow = false;
if($_SERVER["REQUEST_METHOD"] == 'POST'){
$user = $_POST[ 'user'];
$password = $_POST['pass'];
$user = stripcslashes($user);
$password = stripcslashes($password);

$user = mysqli_real_escape_string($conn , $user);
$password = mysqli_real_escape_string($conn , $password);

$sql = "select * from signin where user_name = '$user' and password = '$password'";  

$result = mysqli_query($conn , $sql);
$row = mysqli_fetch_array($result , MYSQLI_ASSOC);

$count = mysqli_num_rows($result);

if($count==1 ){

	session_start();
    $alertShow == false;
	header("Location: index.php?$user");

    exit();

}else{
	header("Location: login.php?$user");
}

}
if($alertShow==true){
echo $alert = '<div class="alert alert-primary" role="alert">
eroare date gresite!
</div>';
}
?>

<?php
session_start();
include '_database.php';
if($_SERVER["REQUEST_METHOD"] == 'POST'){
$user = $_POST[ 'user'];
$password = $_POST['pass'];

$user = stripcslashes($user);
$password = stripcslashes($password);

$user = mysqli_real_escape_string($conn , $user);
$password = mysqli_real_escape_string($conn , $password);


$sql = "select * from signin where user_name = '$user' and password = '$password'";  


$result = mysqli_query($conn , $sql);
$row = mysqli_fetch_array($result , MYSQLI_ASSOC);

$count = mysqli_num_rows($result);

if($count==1 ){
    header("Location: index.php?$user");
    exit();
}else{
    echo '&lt;div class="alert alert-primary" role="alert"&gt;eroare date gresite!&lt;/div&gt;';       
}

}
?>