Some Interview Questions given to me in the past.

1. What is a PostBack?
2. What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState?
3. Demonstrate definition of a property in a class (in c#)
4. Demonstrate populating a dropdownlist from an xml file (in c#)
5. How do you assign a static IP Address to a Windows 2003 Server?
6. Draw out what the outcome of an Inner Join, Left Outer Join and Right Outer Join would be on two tables.
7. How would you access the database connection strings from a web.config file in VS 2003 and VS 2005?
8. Where would you setup “Impersonation” and when would it be a good time to use it?
9. How many static IP Addresses can a Windows 2003 Server have?
10. A client needs a web page that collects the following: first name, last name, phone number and then pushes the data to them via email. Please provide sample code of a form that sends that data to the client.
11. Demonstrate in Asp.Net how to pull a remote user’s IP Address, Referring URL, and the [cookieid] from a user’s machine for domain [SAN].
12. Please provide an example of a time when you have ever used web services.
13. How would you go about debugging a web service SOAP Message?
14. How do you view the methods and properties of a web service within Visual Studio?















1) What is a postback?

http://www.xefteri.com/articles/show.cfm?id=18 does a nice job in explaining what a postback is, in detail.

In my own words: In a standard postback a web page, with a web form is submitted and then processed on the server-side. The server-side then updates the page on the client-side by reposting the data. This is usually seen with something similar to a page refresh. (Which is why, if you are buying something on the web, it's a good idea not to hit refresh button or it would duplicate the last sent request.)

Now with, javascript and nowadays Ajax, it isn't necessary to refresh the whole page. It is possible to just refresh a certain control, allowing the user to see updated information without refreshing and redrawing other controls.



2) What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState?

In my own words:
A viewstate is a serializable hashtable of objects that are used to store information on the client-side. During a postback, the informatin is then used on the server-side before reposting to the client-side. This allows the data found in controls like a textbox to be repoulated, or to use the viewstate to store global variables which can be reused.

A viewstate is stored in base64, and encryption by default is set to auto. This means, as long as no control in the form does not need encryption, then the whole viewstate is unencrypted; otherwise the whole viewstate is encrypted. You can set the view state for each page:

<%@Page ViewStateEncryptionMode="Always" %>

, or you can set it for the whole website by using the web.config:

<configuration>
<system.web>
<pages ViewStateEncryptionMode="Always" />
</system.web>
</configuration>


3) Demonstrate definition of a property in a class

class MyClass
{
private string _name = “”;

public string Name
{
get
{
return _name;
}
set
{
_name = value;
}
}
}


4) Demonstrate populating a dropdownlist from an xml file


Not tested:

XML file:

<library>
<book>
<author>Dietel & Dietel</author>
<title>C how to program</title>
</book>
<book>
<author>William Shakespare</author>
</book>
</library>


XmlDocument doc = new XmlDocument();
doc.Load(Server.MapPath("Library.xml"));
XmlNodeList nodeList = doc.SelectNodes("library/book/"); //xslt path
foreach(XmlNode node in nodeList)
{
DropDownListTitle.Items.Add(new ListItem(node.SelectSingleNode("title").InnerText));
}


5) How do you assign a static IP Address to a Windows 2003 Server?

I personally don't know much about setting up servers, I'm a developer. So, I look it up:
http://technet2.microsoft.com/windowsserver/en/library/36c35b2c-8b8b-4517-812e-913a60ff551d1033.mspx?mfr=true

The basic info provided:

To configure TCP/IP for static addressing
1.
Open Network Connections.
2.
Right-click the network connection you want to configure, and then click Properties.
3.
On the General tab (for a local area connection) or the Networking tab (for all other connections), click Internet Protocol (TCP/IP), and then click Properties.
4.
Click Use the following IP address, and do one of the following:
•
For a local area connection, in IP address, Subnet mask, and Default gateway, type the IP address, subnet mask, and default gateway addresses.
•
For all other connections, in IP address, type the IP address.
5.
Click Use the following DNS server addresses.
6.
In Preferred DNS server and Alternate DNS server, type the primary and secondary DNS server addresses.








6) Draw out what the outcome of an Inner Join, Left Outer Join and Right Outer Join would be on two tables.

Can't draw

7) How would you access the database connection strings from a web.config file in VS 2005? (Don't care about VS 2003 anymore :P )

This question really sucks, I wish it was more specific.

If I just need to look it up, I would just open the web.config file and look in the appSetting tag:

<appSettings>
<add key="sqlConn" value="Server=myPc;Database=Northwind" />
<add key="smtpServer" value="smtp.mydomain.com" />
</appSettings>

If I need to access it in the program:

this.sqlConnection1.ConnectionString = ((string)( System.Configuration.ConfigurationSettings.AppSettings.GetValues("sqlConn.ConnectionString"))));


8) Where would you setup “Impersonation” and when would it be a good time to use it?

Source: http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/4ec9116c-7ca2-4126-9dc4-b7f82b67cd76.mspx?mfr=true

"When using impersonation, ASP.NET applications can optionally execute with the identity of the client on whose behalf they are operating. The usual reason for doing this is to avoid dealing with authentication and authorization issues in the ASP.NET application code. Instead, you rely on Internet Information Services (IIS) to authenticate the user and either pass an authenticated token to the ASP.NET application or, if unable to authenticate the user, pass an unauthenticated token. "

In the web.config:

<identity impersonate="true"/>

http://west-wind.com/weblog/posts/1572.aspx goes in nice detail on how to access information that is not allowed with the standard asp.net permissions.

Lorem Ipsum

I was curious about "Lorem Ipsum", since I have seen this as a subsitution for dummy text. It's a very interesting read.

The use of using this text for dummy text has been around since 1500, which was taken from a book "de Finibus Bonorum et Malorum" (The Extremes of Good and Evil) by Cicero, written in 45 BC.

http://www.lipsum.com/

What is also cool about this site, it has a Lorem Ipsum generator.

How to programatically bind a value to a parameter in a ObjectDataSource

I'm making a guestbook, and one of the values that I'm inserting into the database is the IP address of the user. To get the IP address to bind to the parameter "IP" I added a event that is raised when "Inserting" to the objectdatasource.

From here I just add the value:

protected void ObjectDataSource1_Inserting(object sender, ObjectDataSourceMethodEventArgs e)
{
e.InputParameters["IP"] = Request.UserHostAddress;
}

File Download in ASP.Net

Ok, so I'm making my own site and what I am doing is allowing users on my website to upload and download files. These files are placed into my sql-server database. I was having trouble getting the Response.Write to work, so I went to Response.OutputStream.Write instead.

So on my download page I have:

protected void Page_Load(object sender, EventArgs e)
{
String filepath =
Request.Params.Get("Author") + "-" + Request.Params.Get("Title") + ".mp3";
if
(filepath.Length != 0)
{
Stream readStream =
MusicManager.GetSong(Int32.Parse(Request.Params.Get("file")));
int Length =
256;
Response.Clear();
Response.ContentType =
"application/octet-stream";
Response.AddHeader("Content-Disposition",
"attachment; filename=\"" + filepath + "\"");
Response.Flush();
Byte[]
buffer = new Byte[Length];
int bytesRead = readStream.Read(buffer, 0,
Length);
while (bytesRead > 0)
{
Response.OutputStream.Write(buffer,
0, bytesRead);
bytesRead = readStream.Read(buffer, 0,
Length);
}
Response.End();
readStream.Close();
}
}

Of course I have a page that sends in the query string with the necessary info

This seems all simple when it starts working, but it took me 2 hours to get the file to download correctly.

A good source of information on de-bugging IIS 7 errors

http://mvolo.com/blogs/serverside/archive/2007/07/26/Troubleshoot-IIS7-errors-like-a-pro.aspx

Good source on optimizing SQL Server 2005

http://technet.microsoft.com/en-us/sqlserver/bb331794.aspx

Interview question: What structure would you use to represent shapes in a database?

OK, A few months ago, my friend told me of an interview question that I found interesting. The question that was given to him, paraphrasing: "If you had to set up a database to hold shapes, what would your table structure look like?". The point of the question was for him to convert the concept of a class shape that might be used in an object oriented language to be converted to a database structure. Which is why I was stuck on this question, with no simple straight forward solution.

I then started thinking about this question, again. The idea of the question was to see what tables and columns would you set up to make this feasible. I wanted an easy solution with minimal work, so I avoided the polymorphism concept and went to a simpler definition of a shape (polygon).

I figure I would make 1 table called SHAPE with 2 columns and make the assumption that the shapes are defined as "simple polygons":


ID int, COORDINATES varchar





The ID is obviously the primary key for each shape.


The Coordinates is a order list of Cartesian coordinates going counter-clockwise.

Now, given a shape, the most common questions asked would be what is the perimeter and area of said shape. I could easily make 2 store procedures to find the perimeter and area.

To figure out the perimeter, I just need to add up the distance from each point, simple enough.

To figure out the area of the polygon, I knew there had to be a formula that would do this for me, and thanks to wikipedia I found one:





"The formula was described by Meister in 1769 and by Gauss in 1795. It can be verified by dividing the polygon into triangles".


I was looking around, to see if others seen this question. I did find something similar at http://lists.mysql.com/mysql/207823

If I needed to query the table for certain shapes, then it would be good to add an additional column called: Points int

So, if I needed to query the table for triangles only then I can do a search on points = 3.

Efficient use of Iterators and Delegates

This is a good read. It shows how to effectually use iterators to make garbage collection efficient and to lower memory usage. It also shows how to use delegates to also improve on this concept.

http://msdn2.microsoft.com/en-us/vcsharp/bb264519.aspx

Take the initial uneffecient example:

// First attempt:
public List PeopleIKnowInNewYork()
{
IEnumerable newYorkNumbers = PhoneBook.FindListFor(“New York”);
List peopleIKnow = new List();

foreach ( PhoneBookEntry ph in newYorkNumbers)
{
string name = string.Format(“{0} {1}”, ph.FirstName,
ph.LastName);

if ( RecognizePerson( name ) )
peopleIKnow.Add(name);
}

return peopleIKnow;
}

// Fifth attempt:public

IEnumerable PeopleIKnowInNewYork()
{
IEnumerable newYorkNumbers =
PhoneBook.FindListFor(“New York”);
IEnumerable names = Transform(newYorkNumbers,
delegate(PhoneEntry entry)
{
return string.Format(“{0} {1}”, entry.FirstName, entry.LastName);
});
return Filter(names,
delegate(string name)
{
return RecognizePerson(name);
}
);
}

LINQ and AI?

Well, LINQ is something new to both VB and C# in Visual Studio 8 that allows you to query the data. The data can be XML, ADO.NET, DataSet, or objects. An example of the LINQ format:

var locals = (from c in customers
where c.ZipCode == 91822
select new { FullName = c.FirstName + “ “ +
c.LastName, HomeAddress = c.Address})
.Count();

What I find really interesting about the possibility of using LINQ, is the idea that the program can look at itself in an evaluation. If you add some artificial intelligence, this idea can be a great help in developing programs that can prove themselves correct in logic. I even think, that this concept can be used, with lots of time and planning, to develop a program that can write other programs given a set of parameters and acceptable outcomes.

The concept of using a database like language in a structure language is a very nice concept. If LINQ could be used to select all number of the type Int32 to represent integer numbers, would be something fun to play with. On this subject I might be a little too much in the dream world at the momement, but I do look forward to the possibilities.

Some sources on LINQ:

http://msdn.microsoft.com/msdnmag/issues/07/06/CSharp30/
http://blogs.msdn.com/charlie/archive/2007/07/26/visual-studio-2008-beta-2-released.aspx

Some info on Lambda Calculus:

http://en.wikipedia.org/wiki/Typed_lambda_calculus

Quick Reference: Raise Events in C#

Just wanted to put this down for a quick reference to remember how to raise an event in C#:

Declare:

private delegate void OnMouseOverDelegate(object
sender, System.EventArgs e);
private event OnMouseOverDelegate OnMouseOver;

After InitializeComponent(); :

this.OnMouseOver += new OnMouseOverDelegate(my_MouseHover);

Function:

private void
my_MouseHover(object sender, System.EventArgs e)
{
}