index.php
<!DOCTYPE html>
<html>
<form method="post">
<input type="text" name="address">
<input type="submit" name="submit" value="submit">
</form>
</html>
<?php
if(isset($_POST['submit']))
{
function getLatLong($address){
    if(!empty($address)){
        //Formatted address
        $formattedAddr = str_replace(' ','+',$address);
        //Send request and receive json data by address
        $geocodeFromAddr = file_get_contents
('http://maps.googleapis.com/maps/api/geocode/json?address='.$formattedAddr.'&sensor=false'); 
        $output = json_decode($geocodeFromAddr);
        //Get latitude and longitute from json data
        $data['latitude']  = $output->results[0]->geometry->location->lat; 
        $data['longitude'] = $output->results[0]->geometry->location->lng;
        //Return latitude and longitude of the given address
        if(!empty($data)){
            return $data;
        }else{
            return false;
        }
    }else{
        return false;  
 
    }
}
$address = $_POST['address'];
$latLong = getLatLong($address);
$latitude = $latLong['latitude']?$latLong['latitude']:'Not found';
$longitude = $latLong['longitude']?$latLong['longitude']:'Not found';
echo "Latitude:".$latitude."<br>";
echo "longitude:".$longitude."";
}
?>