I am trying to connect to a db - php

Question

I am trying to connect to a db but I keep getting an error that pops up every chance I get to change the db or connection string . I am currently using php mysqli and wamp will not show any error with the connection itself .
calc.php:
class Login {
var $con;
function __construct($con){
$this->con = $con;
}
function try_connecting(){
$connecting = true;
if($connecting){
if(!$this->con){
die ("Could not connect") . $this->con->connect_errno;
} else {
echo "connected";
}
} else {
return $connecting;
}
}
function try_login(){
if(try_connecting()){
$q = "SELECT username, password FROM persons WHERE username = " . $_POST["username"] . " AND password = " . $_POST['pwd'];
$rows = $this->con->num_rows;
if($rows == 1){
echo "true";
} else {
echo "not user";
}
}
}
}
Here is the test.php:
<?php
include("calc.php");
$u = $_POST['username'];
$p = $_POST['pwd'];
$con = mysqli_connect("localhost","root","","rdb");
$form = new Login($con);
$form->try_connecting();
$form->try_login();
?>
connection string error Unknown database

Answer 1

You forgot to run this query
$q = "SELECT username, password FROM persons WHERE username = " . $_POST["username"] . " AND password = " . $_POST['pwd'];
$rows = $this->con->num_rows;
Try to add
$this->con->query($q)
between the lines above