I have a little problem to check for submit buttons

See more:

C#

C#4.0

I am trying to click on a button on a webpage/website. Whether it is a submit button or preview button or i agree button. The problem i am facing here is that i cannot click on few buttons because some websites have something like this:



and on some sites it is like this:

<button type="submit" name="preview">Preview</button>

In the 2nd example i am able to do the click event easily like this:

private void preview()
       {
           HtmlElement ele = webBrowserCtl.Document.GetElementById("preview");
           if (ele != null)
           {
               ele.InvokeMember("click");
           }
       }

because in 2nd example i can use "name" and can go with it. But in the first code there is no "name" or even any "id" that i can use to find this specific button and clink on it than, it has just the "value". Can you kindly tell me how to do that in the cases like that? how to click on such buttons?
Regards.