Question

When I write the following code:

 Task<string> task = Task.Factory.StartNew<string>(() => "first task")
         .ContinueWith(t =>
                 {
                     Console.WriteLine(t.Result);
                     Console.WriteLine("second task");
                 });

That is wrong!

Then I change it to this:

 var  task = Task.Factory.StartNew<string>(() => "first task")
         .ContinueWith(t =>
                 {
                     Console.WriteLine(t.Result);
                     Console.WriteLine("second task");
                 });

Then everything is OK!

Why?

What is the different between “Task task” and “var task”？

Answer 1

Your line of code returns a Task, not a Task<string> object, because you wrote ContinueWith, not ContinueWith<string>.

A tip that could help you in the future: when you replace a type by var in a variable declaration, you can move your mouse over the var keyword in Visual Studio, a pop-up will be shown with the actual type the var hides in your code.