Want to update my 000webhost website mysql db using android app

Question

I want to update my database having 2 fields serial and ip using an Android app. But it's not updating. When I try to run the app, "Unfortunately App has stopped" pops up on my emulator

My PHP code

<?php
$serial=$_POST["serial"]; 
$ip=$_POST["ip"];

$con=mysqli_connect("mysql9.000webhost.com","~HIDDEN~","password","~HIDDEN~");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

mysqli_query($con,"INSERT INTO ip (serial, ip)
VALUES ('".$serial"', '".$ip"')");


mysqli_close($con);
?>

Main Activity (Android)

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        postData();
    }    
    public void postData() {

        // Create a new HttpClient and Post Header
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost("http://ankit.host56.com/");

        try {
            // Add your data
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
            nameValuePairs.add(new BasicNameValuePair("serial", "23"));
            nameValuePairs.add(new BasicNameValuePair("ip", "24"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            // Execute HTTP Post Request
            HttpResponse response = httpclient.execute(httppost);


        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
        } catch (IOException e) {
            // TODO Auto-generated catch block
        }
    }
}

Layout file

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

</RelativeLayout>