I have a problem converting Mysql to mysqli

I’m getting errors and i don’t know how to change it over to mysqli. Can anyone help me?


<?php
$reg = @$_POST['reg'];
//declaring variables to prevent errors
$fn = ""; //First Name
$ln = ""; //Last Name
$un = ""; //Username
$em = ""; //Email
$em2 = ""; //Email 2
$pswd = ""; //Password
$pswd2 = ""; // Password 2
$d = ""; // Sign up Date
$u_check = ""; // Check if username exists
//registration form
$fn = strip_tags(@$_POST['fname']);
$ln = strip_tags(@$_POST['lname']);
$un = strip_tags(@$_POST['username']);
$em = strip_tags(@$_POST['email']);
$em2 = strip_tags(@$_POST['email2']);
$pswd = strip_tags(@$_POST['password']);
$pswd2 = strip_tags(@$_POST['password2']);
$d = date("Y-m-d"); // Year - Month - Day

if ($reg) {
if ($em==$em2) {
// Check if user already exists
$u_check = mysql_query("SELECT username FROM users WHERE username='$un'");
// Count the amount of rows where username = $un
$check = mysql_num_rows($u_check);
//Check whether Email already exists in the database
$e_check = mysql_query("SELECT email FROM users WHERE email='$em'");
//Count the number of rows returned
$email_check = mysql_num_rows($e_check);
if ($check == 0) {
  if ($email_check == 0) {
//check all of the fields have been filed in
if ($fn&&$ln&&$un&&$em&&$em2&&$pswd&&$pswd2) {
// check that passwords match
if ($pswd==$pswd2) {
// check the maximum length of username/first name/last name does not exceed 25 characters
if (strlen($un)>25||strlen($fn)>25||strlen($ln)>25) {
echo "The maximum limit for username/first name/last name is 25 characters!";
}
else
{
// check the maximum length of password does not exceed 25 characters and is not less than 5 characters
if (strlen($pswd)>30||strlen($pswd)<5) {
echo "Your password must be between 5 and 30 characters long!";
}
else
{
//encrypt password and password 2 using md5 before sending to database
$pswd = md5($pswd);
$pswd2 = md5($pswd2);
$query = mysql_query("INSERT INTO users VALUES ('','$un','$fn','$ln','$em','$pswd','$d','0','Write something about yourself.','','','no')");
die("<h2>Welcome to findFriends</h2>Login to your account to get started ...");
}
}
}
else {
echo "Your passwords don't match!";
}
}
else
{
echo "Please fill in all of the fields";
}
}
else
{
 echo "Sorry, but it looks like someone has already used that email!";
}
}
else
{
echo "Username already taken ...";
}
}
else {
echo "Your E-mails don't match!";
}
}
?>

You need to provide the errors which you are receiving.

considering that you should use prepared statements to prevent SQL Injection (which you currently completely ignore), the database code would need a major rewrite anyways.