How to find latitude and longitude using C#

You could try the NuGet package GoogleMaps.LocationServices, or just spin of its source code. It uses Google's REST API to get lat/long for a given address and vice versa, without the need for an API key.

You use it like this:

public static void Main()
{
    var address = "Stavanger, Norway";

    var locationService = new GoogleLocationService();
    var point = locationService.GetLatLongFromAddress(address);

    var latitude = point.Latitude;
    var longitude = point.Longitude;

    // Save lat/long values to DB...
}

If you want to use the Google Maps API have a look at their REST API, you don't need to install a Google Maps API just send a Request like

http://maps.googleapis.com/maps/api/geocode/xml?address=1600+Amphitheatre+Parkway,+Mountain+View,+CA&sensor=true_or_false

and you will get a response XML.

For response JSON:

https://maps.googleapis.com/maps/api/geocode/json?address=1600+Estância+Sergipe,&key=**YOUR_API_KEY**

For more Information have a look at

https://developers.google.com/maps/documentation/geocoding/index#GeocodingRequests

You can pass address in particular url.. and you get latitude and longitude in return value dt(datatable)

string url = "http://maps.google.com/maps/api/geocode/xml?address=" + address+ "&sensor=false";
WebRequest request = WebRequest.Create(url);

using (WebResponse response = (HttpWebResponse)request.GetResponse())
{
    using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8))
    {
        DataSet dsResult = new DataSet();
        dsResult.ReadXml(reader);
        DataTable dtCoordinates = new DataTable();
        dtCoordinates.Columns.AddRange(new DataColumn[4] { new DataColumn("Id", typeof(int)),
                    new DataColumn("Address", typeof(string)),
                    new DataColumn("Latitude",typeof(string)),
                    new DataColumn("Longitude",typeof(string)) });
        foreach (DataRow row in dsResult.Tables["result"].Rows)
        {
            string geometry_id = dsResult.Tables["geometry"].Select("result_id = " + row["result_id"].ToString())[0]["geometry_id"].ToString();
            DataRow location = dsResult.Tables["location"].Select("geometry_id = " + geometry_id)[0];
            dtCoordinates.Rows.Add(row["result_id"], row["formatted_address"], location["lat"], location["lng"]);
        }
    }
    return dtCoordinates;
}