ASP.NET

Session.Remove("something");

void Page_Load()
{
    if(!Page.IsPostBack)
    {
        Session["something"] = true;
    }
    else
    {
        Session["something"] = false;
    }
}

DateTime? foo;
foo = DateTime.Now;

myVar.dateredeemed = DateTime.Parse("2010-12-03")

1. If the string really comes from user input, they can enter an incorrect value you need to decide whether this should be null or whether the user *must* enter a valid date. Whichever is the correct strategy, incorrect input will throw an error.
2. Can the user enter no date, (i.e. "")? If so you code will not result in null

T M Gray wrote:

You can't assign the filename in an upload control with javascript

string fn = Path.GetFileName(inputFile.PostedFile.FileName);
string savepath = Server.MapPath("Exports") + "\\" + fn;//Exports is a folder where u will save all the posted files...
inputFile.PostedFile.SaveAs(savepath);//makes a copy of the file onto your server...
string[] lines = File.ReadAllLines(savepath);//will read all lines from a file

for (int i = 0; i < lines.Length; i++)//loop through all the lines in your file
{
  //do everything you want with the file contents
}