$url = "http://api.coindesk.com/v1/bpi/currentprice/USD.json";
$price = json_decode(file_get_contents($url));
print $price->{'rate_float'};

----------

$url = "http://api.coindesk.com/v1/bpi/currentprice/USD.json";
$price = json_decode(file_get_contents($url));
$last_price = $price['rate_float'];
echo $last_price;


-------------

$url = "http://api.coindesk.com/v1/bpi/currentprice/USD.json";
$price = json_decode(file_get_contents($url),true);
$last_price = $price['rate_float'];
echo $last_price;