Login and registration pages for a PHP and PDO e-commerce project

We are doing an e-commerce project in a PHP-MySQL combination. Here is the code with PDO we wrote for login and register. I've heard that writing less code is better, so how we can reduce the lines of code?

connection.php

getMessage();
        die();
    }
}
?>

login

        
            Login
            Error:  ' . $login_error_message . '';
            }
            ?>
            
                
                    Username/Email
                    
                
                
                    Password
                    
                
                
                    
                
            
        
    

register

        
            Register
            Error:  ' . $register_error_message . '';
            }
            ?>
            
                
                    Name
                    
                
                
                    Email
                    
                
                
                    Username
                    
                
                
                    Password
                    
                
                
                    
                
            
        
    

Library file to handle request of index.php file

```
Login($username, $password); // check user login
if($user_id > 0)
{
$_SESSION['user_id'] = $user_id; // Set Session
header("Location: profile.php"); // Redirect user to the profile.php
}
else
{
$login_error_message = 'Invalid login details!';
}
}
}

// check Register request
if (!empty($_POST['btnRegister'])) {
if ($_POST['name'] == "") {
$register_error_message = 'Name field is required!';
} else if ($_POST['email'] == "") {
$register_error_message = 'Email field is required!';
} else if ($_POST['username'] == "") {
$register_error_message = 'Username field is required!';
} else if ($_PO

if you really want reduce amount of lines -- delete your comments :)

// start session
session_start();

I can understand that this is start session even without comment, and so on. You should comment some unclear part, some dirty hacks, etc, not every line.

Write comments for every line is anti-pattern, you shouldn't do this. Also less code doesn't mean "better code". I think deleting unnecessary comments is only one case, when this works.

And of course you can minimize your html to one line.

StackExchange Code Review Q#143177, answer score: 3