// PUT api/<controller>/5
 public void Put(int id, Product product)
 {
     var existingProduct = products.FirstOrDefault(p => p.Id == id);
     existingProduct.Name = product.Name;
     existingProduct.Cost = product.Cost;
     existingProduct.Units = product.Units;
 }
        // POST api/<controller>
        public HttpResponseMessage Post(Product product)
        {
            product.Id = products.Max(p => p.Id) + 1;
            products.Add(product);

            HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.Created);
            response.StatusCode = HttpStatusCode.Created;
            string uri = Url.Link("DefaultApi", new { id = product.Id });
            response.Headers.Location = new Uri(uri);
            return response;
        }