What is Marshalling?

Marshaling is a process of making an object in one process (the server) available to another process (the client). There are two ways to achieve the marshalling.
i. Marshal by value: the server creates a copy of the object passes the copy to the client. When a client makes a call to an object marshaled by value (MBV), the server creates an exact copy and sends that copy to the client. The client can then use the object's data and executable functionality directly within its own process or application domain without making additional calls to the server. Objects that the application accesses frequently are best remoted using MBV.
ii. Marshal by reference: the client creates a proxy for the object and then uses the proxy to access the object. When a client makes a call to an object marshaled by reference (MBR), the .NET framework creates a proxy in the client's application domain and the client uses that proxy to access the original object on the server. Large objects that the application accesses relatively infrequently are good candidates for MBR.

Difference between Overloading and Overriding ?

Overloading:
Same function name and different parameters is called overloading.

function ss(int a,int b)

function ss(int a,int b,int d)

Overriding:
The base class method is override by the derived class.

class a
{
private int dd()
{
console.writeline("hai")
}
}

class b inherits a
{
private int dd()
{
console writeline("hai guys")
}
}

the output is
hai guys

What are the types of Authentication?

There are 3 types of Authentication.  Windows, Forms and Passport Authentication.
Windows authentication uses the security features integrated into the Windows NT and Windows XP operating systems to authenticate and authorize Web application users.
Forms authentication allows you to create your own list/database of users and validate the identity of those users when they visit your Web site.
Passport authentication uses the Microsoft centralized authentication provider to identify users. Passport provides a way to for users to use a single identity across multiple Web applications. To use Passport authentication in your Web application, you must install the Passport SDK.

What is Authentication and Authorization?

Authentication is the process of identifying users. Authentication is identifying/validating the user against the credentials (username and password) and Authorization performs after authentication. Authorization is the process of granting access to those users based on identity. Authorization allowing access of specific resource to user.

How a base class method is hidden?

Hiding a base class method by declaring a method in derived class with keyword new. This will override the base class method and old method will be suppressed.

What’s the difference between System.String and System.StringBuilder classes?

System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

What is the difference between const and static readonly?

If you need to alert a user that his session will time out. This is how to do it. Add the following code snippet to the OnInit method on the base page of your application.
protected override void OnInit(EventArgs e)
   {
       base.OnInit(e);
       string script = "window.setTimeout(\"alert('Your session expired!');\", " + (Session.Timeout - 1) * 60000 + ")";
       this.Page.ClientScript.RegisterStartupScript(this.GetType(), "SessionManager", "<script language=\"javascript\">" + script + "</script>");
   }
The difference is that the value of a static readonly field is set at run time, and can thus be modified by the containing class, whereas the value of a const field is set to a compile time constant.
In the static readonly case, the containing class is allowed to modify it only
in the variable declaration (through a variable initializer)
in the static constructor (instance constructors, if it's not static)
static readonly is typically used if the type of the field is not allowed in a const declaration, or when the value is not known at compile time.
Instance readonly fields are also allowed.
Remember that for reference types, in both cases (static and instance) the readonly modifier only prevents you from assigning a new reference to the field. It specifically does not make immutable the object pointed to by the reference.
class Program
{
public static readonly Test test = new Test();
static void Main(string[] args)
{
test.Name = "Program";
test = new Test(); // Error: A static readonly field cannot be assigned to
(except in a static constructor or a variable initializer)
}
}

class Test
{
public string Name;
}
On the other hand, if Test were a value type, then assignment to test.Name would be an error.

How To Add Session Timeout Popup in asp.net

If you need to alert a user that his session will time out. This is how to do it. Add the following code snippet to the OnInit method on the base page of your application.

protected override void OnInit(EventArgs e)

   {

       base.OnInit(e);

       string script = "window.setTimeout(\"alert('Your session expired!');\", " + (Session.Timeout - 1) * 60000 + ")";

       this.Page.ClientScript.RegisterStartupScript(this.GetType(), "SessionManager", "<script language=\"javascript\">" + script + "</script>");

   }

How To Use RegularExpressionValidator with FileUpload control

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="FileUploadTest.aspx.cs" Inherits="FileUploadTest" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

   <title>Untitled Page</title>

</head>

<body>

   <form id="form1" runat="server">

       <div>

           <table cellpadding="0" cellspacing="0" width="100%">

               <tr>

                   <td>

                       Select File</td>

                   <td>

                       <asp:FileUpload ID="fileUpload" runat="Server" /></td>

                   <td>

                       <td align="left">

                           <asp:RegularExpressionValidator runat="server" ID="valUpTest" ControlToValidate="fileUpload"

                               ErrorMessage="Image Files Only (.doc, .txt, .rtf)" ValidationExpression="^(([a-zA-Z]:)|(\\{2}\w+)\$?)(\\(\w[\w].*))(.doc|.txt|.rtf)$" />

                       </td>

                   </td>

               </tr>

               <tr>

                   <td colspan="2" align="Center">

                       <asp:Button ID="btnSubmit" runat="Server" Text="Submit" OnClick="btnSubmit_Click" />

                   </td>

               </tr>

           </table>

       </div>

   </form>

</body>

</html>

using System;

using System.Data;

using System.Configuration;

using System.Collections;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.IO;

public partial class FileUploadTest : System.Web.UI.Page

{

   string sPath = "Image";

   protected void Page_Load(object sender, EventArgs e)

   {

   }

   protected void btnSubmit_Click(object sender, EventArgs e)

   {

       if (fileUpload.HasFile)

       {

           fileUpload.PostedFile.SaveAs(Server.MapPath(sPath) + "/" + Path.GetFileName(fileUpload.PostedFile.FileName));

       }

   }

}

differences between INSERT select and insert into select?

INSERT INTO Store_Information (store_name, Sales, Date)

SELECT store_name, Sales, Date

FROM Sales_Information