Problem with assigning variable C#

When I return the string timeTaken, it is null, and it says this on the IDE to, although it has been defined in the main method (TimeSpan timeTaken = timer.Elapsed;)

class Program
{    
    public static string timeTaken;    

    static void Main(string[] args)
    {                
        HttpWebRequest request = (Htt开发者_如何学PythonpWebRequest)WebRequest.Create(firstline);    
        Stopwatch timer = new Stopwatch();
        timer.Start();               
        using (var response = request.GetResponse());
        timer.Stop();    
        TimeSpan timeTaken = timer.Elapsed;
        ...
    }
}            

How can I output timeTaken?

---

You define a local variable with the same name

TimeSpan timeTaken

which hides your static class field.

To output the value of timer.Elapsed you could write something like this:

Console.WriteLine("{0}", timer.Elapsed);

---

There is two timeTaken variable, one local to rthe Main function, the other one is a static member of the class. To explicitly refer to the string one use Program.timeTaken. Anyway is better if you refactor the code to have different names.

---

You probably want something more like this:-

class Program
{
  public static string timeTaken;
  static void Main(string[] args)
  {
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(firstline);
    System.Diagnostics.Stopwatch timer = new Stopwatch();
    timer.Start();
    using (var response = request.GetResponse())
    timer.Stop();
    timeTaken = timer.Elapsed.ToString();
  }
}

---

You made a simple mistake: you define the variable "timeTaken" once again inside static void Main(...) on the line

TimeSpan timeTaken = timer.Elapsed;

This will shadow the static definition. To get back to the static class field use

Program.timeTaken = ...

think about naming (for example name your static field _timeTaken or just use

timeTaken = timer.Elapsed;

instead of

TimeSpan timeTaken = timer.Elapsed;