Mysql bind: number of elements do not match - php

Question

I can't fathom where I went wrong on this instruction. I keep getting the warning that number of elements does not match the bind value.
I'm trying to validate a field for country where users can select the country they are registering from but whenever I run a test on xampp I get the warning whilst the information aren't sent to the database.
I'm not sure if my code is liable to sql injections since I'm new to php and mysql. If i remove the country function the form works properly. I think the error is from the html form so I'd rather not uploaded it here.
Here's the php code.
<?php
// Include config file
require_once "db.php";
// Define variables and initialize with empty values
$username = $password = $confirm_password = $country = "";
$username_err = $password_err = $confirm_password_err = $country_err = "";
// Processing form data when form is submitted
if($_SERVER["REQUEST_METHOD"] == "POST"){
// Validate username
if(empty(trim($_POST["username"]))){
$username_err = "Please enter a username.";
} else{
// Prepare a select statement
$sql = "SELECT id FROM users WHERE username = ?";
if($stmt = mysqli_prepare($db, $sql)){
// Bind variables to the prepared statement as parameters
mysqli_stmt_bind_param($stmt, "s", $param_username);
// Set parameters
$param_username = trim($_POST["username"]);
// Attempt to execute the prepared statement
if(mysqli_stmt_execute($stmt)){
/* store result */
mysqli_stmt_store_result($stmt);
if(mysqli_stmt_num_rows($stmt) == 1){
$username_err = "This username is already taken.";
} else{
$username = trim($_POST["username"]);
}
} else{
echo "Oops! Something went wrong. Please try again later.";
}
// Close statement
mysqli_stmt_close($stmt);
}
}
// Validate password
if(empty(trim($_POST["password"]))){
$password_err = "Please enter a password.";
} elseif(strlen(trim($_POST["password"])) < 6){
$password_err = "Password must have atleast 6 characters.";
} else{
$password = trim($_POST["password"]);
}
// Validate confirm password
if(empty(trim($_POST["confirm_password"]))){
$confirm_password_err = "Please confirm password.";
} else{
$confirm_password = trim($_POST["confirm_password"]);
if(empty($password_err) && ($password != $confirm_password)){
$confirm_password_err = "Password did not match.";
}
}
// Validate Country
if(empty(trim($_POST["country"]))){
$country_err = "Please Choose a Country.";
}
else{
$country = trim($_POST["country"]);
}
// Check input errors before inserting in database
if(empty($username_err) && empty($password_err) && empty($confirm_password_err)){
// Prepare an insert statement
$sql = "INSERT INTO users (username, password, country) VALUES (?, ?, ?)";
if($stmt = mysqli_prepare($db, $sql)){
// Bind variables to the prepared statement as parameters
mysqli_stmt_bind_param($stmt, "ss", $param_username, $param_password, $param_country);
// Set parameters
$param_country = $country;
$param_username = $username;
$param_password = password_hash($password, PASSWORD_DEFAULT); // Creates a password hash
// Attempt to execute the prepared statement
if(mysqli_stmt_execute($stmt)){
// Redirect to login page
header("location: login.php");
} else{
echo "Something went wrong. Please try again later.";
}
// Close statement
mysqli_stmt_close($stmt);
}
}
// Close connection
mysqli_close($db);
}
?>.`

Answer 1

I can see a couple of things:
Your check for input errors does not check if "country_err" is empty.
Your mysqli_stmt_bind_param only defines types for 2 fields, "ss", but you are passing in 3 fields so it should be "sss"