How to Use MVC Controller and WebAPI Controller in same project

You can write both configurations in the same file like this:

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index",
                id = UrlParameter.Optional }
        );
    }

    public static void Register(HttpConfiguration config)
    {
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

In the Global.aspx file, edit your code like this:

protected void Application_Start()
{
   AreaRegistration.RegisterAllAreas();
   GlobalConfiguration.Configure(RouteConfig.Register); // WEB API 1st
   FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
   RouteConfig.RegisterRoutes(RouteTable.Routes); // MVC 2nd
   BundleConfig.RegisterBundles(BundleTable.Bundles);
} 

You need to register the routing for web api BEFORE registering the routing for MVC, so basically your App_Start()function should look like this:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    GlobalConfiguration.Configure(WebApiConfig.Register);//WEB API 1st
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);//MVC 2nd
    BundleConfig.RegisterBundles(BundleTable.Bundles);
}