Link a php page to another php page - php

Question

I am trying to link a make a login page using php without database but the link to the other page is not working . It is staying on the same page. No error message also.
Here is the php part of the code:
<?php
$error = "";
if(isset($_POST['MRDlogin']))
{
if(isset($_POST['username'],$_POST['password'])){
/*** You can change username & password ***/
$user = array(
"user" => "MRD",
"pass"=>"msit"
);
$username = $_POST['username'];
$pass = $_POST['password'];
if($username == $user['user'] && $pass == $user['pass']){
header("Location: http://localhost/portal/MRD.php");
}else{
$error = '<div class="alert alert-danger">Invalid Login</div>';
}
}
}
and my html form part is:
> <div class="panel-body">
> <?php echo $error; ?>
> <form accept-charset="UTF-8" role="form" method="post">
> <fieldset>
> <div class="form-group">
> <input class="form-control" placeholder="Username" name="username" type="text">
> </div>
> <div class="form-group">
> <input class="form-control" placeholder="Password" name="password" type="password" value="">
> </div>
> <input class="btn btn-lg btn-success btn-block" type="submit" value="Login">
> </fieldset>
> </form>
> </div>

Answer 1

The following variable cannot be found
$_POST['MRDlogin']
Add it in you button as shown below
<div class="panel-body">
<?php echo $error; ?>
<form accept-charset="UTF-8" action="page.php" role="form" method="post">
<fieldset>
<div class="form-group">
<input class="form-control" placeholder="Username" name="username" type="text">
</div>
<div class="form-group">
<input class="form-control" placeholder="Password" name="password" type="password" value="">
</div>
<input class="btn btn-lg btn-success btn-block" type="submit" value="Login" name="MRDlogin">
</fieldset>
</form>

Answer 2

in form tag add action tag with value of page name that will process submited form:
<form action="page.php" accept-charset="UTF-8" role="form" method="post">