AspNetWebApiSample/SampleWebApi/Controllers/ValuesController.cs

ValuesController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace SampleWebApi.Controllers
{
    public class ValuesController : ApiController
    {
        static readonly List<string> values = new List<string> { "value0", "value1" };

        public string Get(int id)
        {
            if (id < 0 || values.Count <= id)
            {
                var message = $"No value with ID = {id}";
                throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound, message));

                // No content:
                //throw new HttpResponseException(HttpStatusCode.NotFound);
            }
            return values[id];
        }
    }
}