Error creating login system php - php

Question

I've been trying to create a php login system but I can't make it work as if I try to login with valid username and password it will say "fail". I've using this technique before and was successful but this time I can't make it work.
Code:
<?php
$username=$_POST['username'];
$password=$_POST['password'];
$conn = new PDO("mysql:host=localhost;dbname=login" ,'root','');
if (!$conn){
die("Not connected". mysqli_connect_error());
}else {
echo "Connection sucessfull";
echo "</br>";
}
$sql = "select * from details where Username=$username and Password=$password";
$stmt=$conn->prepare($sql);
$stmt->bindparam("Username",$username,PDO::PARAM_STR);
$stmt->bindparam("Password",$password,PDO::PARAM_STR);
$stmt->execute();
$num = $stmt->rowCount();
if ($num>0){
echo "You are logged in";
}else {
echo "fail";
}
Thanks

Answer 1

Your statement should go like this:
$stmt= $conn->prepare("SELECT * FROM `details`
WHERE `Username`=:username AND `Password`=:password");
$stmt->bindParam(':username', $username, PDO::PARAM_STR);
$stmt->bindParam(':password', $password, PDO::PARAM_STR);
$stmt->execute();
Note:
According to php.net PDOStatement::rowCount() returns the number of
rows affected by the last DELETE, INSERT, or UPDATE statement executed
by the corresponding PDOStatement object.
So for counting the number of rows returned by select statement, you can use fetchAll():
if (count($stmt->fetchAll()) > 0) {
echo "You are logged in";
}else {
echo "fail";
}
And for setting smart PDO connection:
try {
$db_host = '';// hostname
$db_name = '';// databasename
$db_user = '';// username
$user_pw = '';// password
$conn = new PDO('mysql:host='.$db_host.'; dbname='.$db_name, $db_user, $user_pw);
$conn->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
$conn->exec("SET CHARACTER SET utf8");
}catch (PDOException $err) {
echo "harmless error message if the connection fails";
$err->getMessage() . "<br/>";
file_put_contents('PDOErrors.txt',$err, FILE_APPEND);//log errors
die(); // terminate connection
}

Answer 2

I've formatted your code and it should work now. You cannot mix mysqli_* with PDO.
$conn = new pdo("mysql:host=localhost;dbname=login;", 'root', '');
if ($conn->connect_error) {
die("Not connected" . $conn->connect_error);
}
echo "Connection successful<br/>";
$sql= "select * from details where Username=:username and Password=:password";
$result = $connection->prepare($sql);
$result->bindParam(":username" ,$_POST['username']);
$result->bindParam(":password" ,$_POST['password']);
$result->execute();
$num=$result->fetchColumn();
if($num > 0){
header("location:index.php");
}else{
header("location:login.php");
}