Untitled

<form action="main_login.php" method="post" style="text-align:right;">
    Username:
    <input type="text" name="username" value="" size=20  style="display:inline-block;margin-left:10px"required>
    <br>
    Password:
    <input type="password" name="password" value="" size=20 style="margin-left:12px"required>
    <br>
    <input type="submit" value="Log In" style="margin-left:75px"=>
</form>

<?php
    session_start();
    $con = mysqli_connect("localhost", "root", "", "complaints");
    if (!$con) {
        die('Could not connect: ' . mysql_error());
    }
    $myusername=$_POST["username"];
    $mypassword=$_POST["password"];
    echo $myusername . "<br>";
    echo $mypassword . "<br>";


    // MySQL injection
    $myusername = stripslashes($myusername);
    $mypassword = stripslashes($mypassword);
    $myusername = mysql_real_escape_string($myusername);
    $mypassword = mysql_real_escape_string($mypassword);
    $sql="SELECT * FROM register WHERE username='$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"
    $_SESSION['username']=$myusername;
    $_SESSION['password']=$mypassword;
    header("location:login_success.php");
    }
    else {
    echo "Wrong Username or Password";
    }
    mysqli_close($con);
?>

<?php
    session_start();
    if ( isset( $_SESSION['username'] ) ){
    header("location:main_login.php");
    }
?>

<html>
<body>
    Login Successful
</body>
</html>

$myusername=$_POST["username"];
$mypassword=$_POST["password"];

$myusername=$_POST["username"];
$mypassword=$_POST["password"];

$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);

$myusername = mysqli_real_escape_string($con,$myusername);
$mypassword = mysqli_real_escape_string($con,$mypassword);

$myusername = mysqli_real_escape_string($con,$_POST['username']);
$mypassword = mysqli_real_escape_string($con,$_POST['password']);

header("location:login_success.php");
exit;

$myusername=$_POST["username"];
$mypassword=$_POST["password"];
echo $myusername . "<br>";
echo $mypassword . "<br>";

$myusername = stripslashes($_POST["username"]);
$mypassword = stripslashes($_POST["password"]);
$myusername = mysqli_real_escape_string($con,$_POST['username']);
$mypassword = mysqli_real_escape_string($con,$_POST['password']);

<form action="main_login.php" method="post" style="text-align:right;">
    Username:
    <input type="text" name="username" value="" size=20  style="display:inline-block;margin-left:10px"required>
    <br>
    Password:
    <input type="text" name="password" value="" size=20 style="margin-left:12px"required>
    <br>
    <input type="submit" value="Log In" style="margin-left:75px"=>
</form>

<?php

    $DB_HOST = 'xxx';
    $DB_USER = 'xxx';
    $DB_PASS = 'xxx';
    $DB_NAME = 'xxx';

    $conn = new mysqli($DB_HOST, $DB_USER, $DB_PASS, $DB_NAME);
    if($conn->connect_errno > 0) {
      die('Connection failed [' . $conn->connect_error . ']');
    }

    $myusername = stripslashes($_POST["username"]);
    $mypassword = stripslashes($_POST["password"]);
    $myusername = mysqli_real_escape_string($conn,$_POST['username']);
    $mypassword = mysqli_real_escape_string($conn,$_POST['password']);


    echo $myusername; // echos
    echo "<br>";
    echo $mypassword; // echos


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

    $count=mysqli_num_rows($result);

    if($count==1){
        echo "Yep";
    }
    else{
        echo "nope";
    }

<?php
session_start();

<?php session_start();