call HttpPost method from Client in C# (http://stackoverflow.com/questions/26990773/call-httppost-method-from-client-in-c-sharp-code/26990889#26990889)

HttpClient.cs

using (var client = new HttpClient())
{
    var values = new List<KeyValuePair<string, string>>();
    values.Add(new KeyValuePair<string, int>("n", "42"));
    values.Add(new KeyValuePair<string, string>("s", "string value"));

    var content = new FormUrlEncodedContent(values);

    var response = await client.PostAsync("http://www.domain.org/receiver.aspx", content);

    var responseString = await response.Content.ReadAsStringAsync();
}

HttpWebRequest.cs

var request = (HttpWebRequest)WebRequest.Create("http://www.domain.org/receiver.aspx");

var postData = "n=42&s=string value";
var data = Encoding.ASCII.GetBytes(postData);

request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = data.Length;

using (var stream = request.GetRequestStream())
{
    stream.Write(data, 0, data.Length);
}

var response = (HttpWebResponse)request.GetResponse();
var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

WebClient.cs

using (var wb = new WebClient())
{
    var data = new NameValueCollection();
    data["n"] = "42";
    data["s"] = "string value";

    var response = wb.UploadValues("http://www.domain.org/receiver.aspx", "POST", data);
}

WebRequest.cs

WebRequest request = WebRequest.Create ("http://www.domain.org/receiver.aspx");
request.Method = "POST";
string postData = "n=42&s=string value";
byte[] byteArray = Encoding.UTF8.GetBytes (postData);
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = byteArray.Length;
Stream dataStream = request.GetRequestStream ();
dataStream.Write (byteArray, 0, byteArray.Length);
dataStream.Close ();

//Response
WebResponse response = request.GetResponse ();
Console.WriteLine (((HttpWebResponse)response).StatusDescription);
dataStream = response.GetResponseStream ();
StreamReader reader = new StreamReader (dataStream);
string responseFromServer = reader.ReadToEnd ();
Console.WriteLine (responseFromServer);
reader.Close ();
dataStream.Close ();
response.Close ();