I tried above solutions but none was working then i tried to fix on my own so below is the correct code:
$going=$this->input->post('going');
$address =$going; // Google HQ
$prepAddr = str_replace(' ','+',$address);
$apiKey = 'Add your API Key'; // Google maps now requires an API key.
$geocode=file_get_contents('https://maps.googleapis.com/maps/api/geocode/json?
address='.urlencode($address).'&sensor=false&key='.$apiKey);
//print_r($geocode);
$output= json_decode($geocode);
$latitude = $output->results[0]->geometry->location->lat;
$longitude = $output->results[0]->geometry->location->lng;