How to get a variable value from the address of a page like .aspx?pid=84

Hi,
One of my page has address www.example.com/testquery.aspx
My requirement is that if someone writes in address bar as www.example.com/testquery.aspx?pid=84 then I want to store the value of pid into some other variable and then show the content of that testquery page according to that value, and if there is not any value i.e. the user enter only www.example.com/testquery.,aspx then load the default page of testquery.
I tried like

Dim start As String     start = querystring("pid")     newstring.Text = startDim start A ...