.NET (Core and Framework)

Hi Programmers,

Have you ever practiced coding online to prepare a technical interview or to groom your skills? If yes, how well it was? Which websites have you used? And, how effective they were? If possible, share the challenges you have faced?

Dim text2 As String = ""
Dim num As Integer = 1
Dim num2 As Integer
Dim num3 As Integer
Do
    ' The following expression was wrapped in a unchecked-expression
    Dim value As Integer = CInt(Math.Round(Math.Floor(CDbl((10.0F * VBMath.Rnd())))))
    text2 += Conversions.ToString(value)
    num += 1
    num2 = num
    num3 = 8
Loop While num2 <= num3

protected void GetArticleCount()
{
    ArticlesManager articlesManager = new ArticlesManager();
    ViewBag.ArticlesCount = articlesManager.ArticleCount();
}

var t1 = Task.Factory.StartNew(() => GetArticleCount());
var t2 = Task.Factory.StartNew(() => GetBrancheCount());
var t3 = Task.Factory.StartNew(() => GetCompaniesCount());
var t4 = Task.Factory.StartNew(() => GetDeliveriesCount());
var t5 = Task.Factory.StartNew(() => GetDistributionCentresCount());
var t6 = Task.Factory.StartNew(() => GetDocksCount());
var t7 = Task.Factory.StartNew(() => GetInvoicesCount());
var t8 = Task.Factory.StartNew(() => GetOrdersCount());

var taskList = new List<Task> { t1, t2, t3, t4, t5, t6, t7, t8 };
Task.WaitAll(taskList.ToArray());

Exception Details: System.FormatException: The format of value 'application/json; charset=utf-8' is invalid.

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

[FormatException: The format of value 'application/json; charset=utf-8' is invalid.]
   System.Net.Http.Headers.MediaTypeHeaderValue.CheckMediaTypeFormat(String mediaType, String parameterName) +119919
   System.Net.Http.Headers.MediaTypeHeaderValue..ctor(String mediaType) +23
   System.Net.Http.ObjectContent.BuildHeaderValue(String mediaType) +63
   System.Net.Http.ObjectContent`1..ctor(T value, MediaTypeFormatter formatter, String mediaType) +66
   System.Net.Http.HttpRequestMessageExtensions.CreateResponse(HttpRequestMessage request, HttpStatusCode statusCode, T value, HttpConfiguration configuration) +892
   System.Net.Http.HttpRequestMessageExtensions.CreateResponse(HttpRequestMessage request, HttpStatusCode statusCode, T value) +104
   System.Web.Http.Dispatcher.HttpControllerDispatcher.HandleException(HttpRequestMessage request, Exception exception, HttpConfiguration configuration) +191
   System.Web.Http.Dispatcher.HttpControllerDispatcher.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +284
   System.Net.Http.DelegatingHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +41
   System.Web.Http.HttpServer.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +347
   System.Net.Http.HttpMessageInvoker.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) +55
   System.Web.Http.WebHost.HttpControllerHandler.BeginProcessRequest(HttpContextBase httpContextBase, AsyncCallback callback, Object state) +316
   System.Web.Http.WebHost.HttpControllerHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +77
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +103
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

I searched in google but can't find the proper solution.

Please help me