public IssueBook(int sid, int bid)
{
Sid = sid;
Bid = bid;
IssueDate = DateTime.Now;
Returndate = IssueDate.AddDays(30);
// TODO: this keyword are not used.
//IssueDate = issueDate; //TODO: Set today's date as issue date
//Returndate = returndate; // TODO: Calculate retrun date based on issue date
}