HttpWebRequest.ContentType Property

            // Set the 'Method' property of the 'Webrequest' to 'POST'.
            myHttpWebRequest.Method = "POST";
            Console.WriteLine ("\nPlease enter the data to be posted to the (http://www.contoso.com/codesnippets/next.asp) Uri :");

            // Create a new string object to POST data to the Url.
            string inputData = Console.ReadLine ();


            string postData = "firstone=" + inputData;
            ASCIIEncoding encoding = new ASCIIEncoding ();
            byte[] byte1 = encoding.GetBytes (postData);

            // Set the content type of the data being posted.
            myHttpWebRequest.ContentType = "application/x-www-form-urlencoded";

            // Set the content length of the string being posted.
            myHttpWebRequest.ContentLength = byte1.Length;

            Stream newStream = myHttpWebRequest.GetRequestStream ();

            newStream.Write (byte1, 0, byte1.Length);
            Console.WriteLine ("The value of 'ContentLength' property after sending the data is {0}", myHttpWebRequest.ContentLength);

            // Close the Stream object.
            newStream.Close ();