php - currency converter

<?php 
// Fetching JSON
$req_url = 'https://api.exchangerate-api.com/v4/latest/USD';
//$req_url = 'https://api.exchangerate-api.com/v4/latest/EUR';
$response_json = file_get_contents($req_url);

// Continuing if we got a result
if(false !== $response_json) {

    // Try/catch for json_decode operation
    try {

	// Decoding
	$response_object = json_decode($response_json);

	// YOUR APPLICATION CODE HERE, e.g.
	$base_price = 1; // Your price in USD
	

	if(isset($_POST['submit'])) 
		{ 
		    $base_price = isset($_POST['price'])?$_POST['price']:1;
		    $rate = isset($_POST['rates'])?$_POST['rates']:1;
		    $EUR_price = round(($base_price * $rate), 2);

			echo "Rate: ". $EUR_price;
		   
		   
		}
	

    }
    catch(Exception $e) {
        // Handle JSON parse error...
    }

}


?>
<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
   <input type="text" name="price"><br>
   <select name="rates">

   	<?php foreach ($response_object->rates as $key => $value) { ?>
   		 <option value="<?php echo $value; ?>"><?php echo $key; ?></option>
   	<?php } ?>
     
 
 
   </select>
   <input type="submit" name="submit" value="Submit "><br>
</form>