PHP error problem collection

1. The single quotes surrounding $pswd1 and $pswd2 cannot be deleted, otherwise data cannot be inserted into MySQL.

<?php
$con=mysql_connect("localhost","root","00001111");
if(!$con){
    die("Could not connect MySQL database!");
}
mysql_select_db("sql_test",$con);
$pswd1=md5("0000");
$pswd2=md5("1111");
$sql="INSERT INTO logins (username,pswd)
VALUES
('John','$pswd1'),
('Sam','$pswd2')";
mysql_query($sql,$con);
mysql_close($con);
?>

2.Linux: The newline character in the file is "n"; Windows: The newline character in the file is "rn";

Example: File-based authentication

File authenticationFile. The content of txt is as follows:

jack:ae2bac2e4b4da805d01b2952d7e35ba4
milk:ae2bac2e4b4da805d01b2952d7e35ba4

<?php
$authorized=false;
if(isset($_SERVER['PHP_AUTH_USER'])&&isset($_SERVER['PHP_AUTH_PW'])){
    $authFile=file("authenticationFile.txt");
    if(in_array($_SERVER['PHP_AUTH_USER'].":"
        .md5($_SERVER['PHP_AUTH_PW'])."\n",$authFile)){
        $authorized=true;
    }
}
if(!$authorized){
    header('WWW-Authenticate:Basic Realm="Secret Stash"');
    header('HTTP/1.0 401 Unauthorized');
    print('You must provide the proper credentials');
    exit;
}
?>

If it is in a Windows environment, the above code "n" needs to be changed to "rn"

The above has introduced the collection of PHP error problems, including aspects of the problem. I hope it will be helpful to friends who are interested in PHP tutorials.