Count function is not working properly for sql's result - php

Question

I wrote code for sign up where I check username , if it is exists in database or not than add new user accordingly. I am new to sql->prepare statement, Problem is in count function , when checking username it works properly, but in else part when adding user it gives me following error
Uncaught TypeError: count(): Argument #1 ($value) must be of type
Countable|array, bool
Here is my adduser.php code.
<?php
include 'config.php';
//checkusername
$check = $con->prepare("select username from users where username = ?");
$check->bindParam(1,$username);
$username = $_POST['username'];
$check->execute();
$row = $check->fetch(PDO::FETCH_ASSOC);
if(count($row)){
echo -1;
}
else{
$sql = $con->prepare("insert into users(name,username,password) values(?,?,?)");
$sql->bindParam(1,$name);
$sql->bindParam(2,$username);
$sql->bindParam(3,$password);
$name = $_POST['name'];
$username = $_POST['username'];
$password = md5($_POST['password']);
$sql->execute();
echo 1;
}
?>

Answer 1

It doesn't make much sense to use count here, you don't need to know how many fields are in the row.
Just check if it's false or not - see php.net/manual/en/pdostatement.fetch.php which mentions that fetch() will return false when it fails (i.e. there is no row available).
This would make more sense:
if($row) {
$sql = $con->prepare("insert into users(name,username,password) values(?,?,?)");
//...etc...
}
else {
echo -1;
}

Answer 2

After executing the query with $check->execute();, you can use the built-in method to count the returned rows: $check->rowCount();.
I think the statement above returned 0 rows, so you can't do $check->fetch() and it returns false.
Example:
// Your code here...
$check = $con->prepare("select username from users where username = ?");
$username = $_POST['username']; // This line needs to be before the next one, because you used the variable $username before defining it
$check->bindParam(1,$username);
$check->execute();
if($check->rowCount() > 0) {
// User does exist
} else {
// User does not exist
}

Answer 3

Edit 2: I just realised that the answer I've given below is wrong. The thing I suggest instead is checking if there's any value by using the PDO rowCount() method, like this: if ($check->rowCount()>0)
wrong stuff below
You're assigining $username a value after binding it.
$check = $con->prepare("select username from users where username = ?");
$check->bindParam(1,$username); //bind $username
$username = $_POST['username']; //assign value
$check->execute();
Try switching those two lines so $username is assigned a value when you're binding it.
$check = $con->prepare("select username from users where username = ?");
$username = $_POST['username']; //assign value
$check->bindParam(1,$username); //bind $username
$check->execute();
Edit
In case you're still having issues, try checking if there's any error in the sql statement execution.
After your $check->execute(); you can add print_r($check->errorInfo()); to see if your MySQL statement has any issues in it.