<?php
ob_start();
$host="localhost"; // Host name
$username="xxxxx"; // Mysql username
$password="xxxx="; // Mysql password
$db_name="xxxx"; // Database name
$tbl_name="xxxx"; // Table name

// Connect to server and select databse.
$con = new mysqli("$host", "$username", "$password","$db_name")or die("cannot connect");

// Define $myusername and $mypassword
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];

// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysqli_real_escape_string($con , $myusername);
$mypassword = mysqli_real_escape_string($con , $mypassword);

$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysqli_query($con , $sql);

// Mysql_num_row is counting table row
$count=mysqli_num_rows($result);
// If result matched $myusername and $mypassword, table row must be 1 row

if($count==1){
// Register $myusername, $mypassword and redirect to file "login_success.php"

$_SESSION['myusername']= "$myusername";
$_SESSION['mypassword']= "$mypassword";
header("location:login_success.php");
}
else {
echo "Wrong username or password!";
}

ob_end_flush();
?>