problem in vb to C# converter

Question

hi all
i hava a piece vb code
i convert it to c# but when it convert to C# i have error in my program
can anybody help me?

vb code(this code is true)
Do Until vreadyState = 4
                  Application.DoEvents()
                  vreadyState = Me.WebBrowser1.ReadyState
            Loop
            Dim eleminput As HtmlElementCollection
            Dim DocCol As HtmlDocument
            DocCol = WebBrowser1.Document
            eleminput = DocCol.GetElementsByTagName("input")


c# code
for (; (vreadystate == 4); )
                  {
                        Application.DoEvents();
                        vreadystate = Convert.ToInt32(this.webBrowser1.ReadyState);

                  }
                  HtmlElementCollection eleminput = default(HtmlElementCollection);
                  HtmlDocument DocCol = default(HtmlDocument);
                  DocCol = webBrowser1.Document;
                  eleminput =DocCol.GetElementsByTagName("input");

run this code
but my program has error in last line
"Object reference not set to an instance of an object."

how to change this code that solve this error?