C# Interview Questions and Answers

1. What’s the implicit name of the parameter that gets passed into the class’ set method?
   Value, and its datatype depends on whatever variable we’re changing.
2. How do you inherit from a class in C#?
   Place a colon and then the name of the base class. Notice that it’s double colon in C++.
3. Does C# support multiple inheritance?
   No, use interfaces instead.
4. When you inherit a protected class-level variable, who is it available to?
   Classes in the same namespace.
5. Are private class-level variables inherited?
   Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.
6. Describe the accessibility modifier protected internal.
   It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
7. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write? Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.
8. What’s the top .NET class that everything is derived from?
   System.Object.
9. How’s method overriding different from overloading?
   When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.
10. What does the keyword virtual mean in the method definition?
    The method can be over-ridden.
11. Can you declare the override method static while the original method is non-static?
    No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
12. Can you override private virtual methods?
    No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
13. Can you prevent your class from being inherited and becoming a base class for some other classes?
    Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.
14. Can you allow class to be inherited, but prevent the method from being over-ridden?
    Yes, just leave the class public and make the method sealed.
15. What’s an abstract class?
    A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.
16. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
    When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.
17. What’s an interface class?
    It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
18. Why can’t you specify the accessibility modifier for methods inside the interface?
    They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
19. Can you inherit multiple interfaces?
    Yes, why not.
20. And if they have conflicting method names?
    It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
21. What’s the difference between an interface and abstract class?
    In the interface all methods must be abstract; in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.
22. How can you overload a method?
    Different parameter data types, different number of parameters, different order of parameters.
23. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor?
    Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
24. 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.
25. What’s the advantage of using System.Text.StringBuilder over System.String?
    StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.
26. Can you store multiple data types in System.Array?
    No.
27. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
    The first one performs a deep copy of the array, the second one is shallow.
28. How can you sort the elements of the array in descending order?
    By calling Sort() and then Reverse() methods.
29. What’s the .NET datatype that allows the retrieval of data by a unique key?
    HashTable.
30. What’s class SortedList underneath?
    A sorted HashTable.
31. Will finally block get executed if the exception had not occurred?
    Yes.
32. What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception?
    A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.
33. Can multiple catch blocks be executed?
    No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.
34. Why is it a bad idea to throw your own exceptions?
    Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.
35. What’s a delegate?
    A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
36. What’s a multicast delegate?
    It’s a delegate that points to and eventually fires off several methods.
37. How’s the DLL Hell problem solved in .NET?
    Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.
38. What are the ways to deploy an assembly?
    An MSI installer, a CAB archive, and XCOPY command.
39. What’s a satellite assembly?
    When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.
40. What namespaces are necessary to create a localized application?
    System.Globalization, System.Resources.
41. What’s the difference between // comments, /* */ comments and /// comments?
    Single-line, multi-line and XML documentation comments.
42. How do you generate documentation from the C# file commented properly with a command-line compiler?
    Compile it with a /doc switch.
43. What’s the difference between <c> and <code> XML documentation tag?
    Single line code example and multiple-line code example.
44. Is XML case-sensitive?
    Yes, so <Student> and <student> are different elements.
45. What debugging tools come with the .NET SDK?
    CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.
46. What does the This window show in the debugger?
    It points to the object that’s pointed to by this reference. Object’s instance data is shown.
47. What does assert() do?
    In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.
48. What’s the difference between the Debug class and Trace class? Documentation looks the same.
    Use Debug class for debug builds, use Trace class for both debug and release builds.
49. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
    The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.
50. Where is the output of TextWriterTraceListener redirected?
    To the Console or a text file depending on the parameter passed to the constructor.
51. How do you debug an ASP.NET Web application?
    Attach the aspnet_wp.exe process to the DbgClr debugger.
52. What are three test cases you should go through in unit testing?
    Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).
53. Can you change the value of a variable while debugging a C# application?
    Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.
54. Explain the three services model (three-tier application).
    Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
55. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?
    SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.
56. What’s the role of the DataReader class in ADO.NET connections?
    It returns a read-only dataset from the data source when the command is executed.
57. What is the wildcard character in SQL? Let’s say you want to query database with LIKE for all employees whose name starts with La.
    The wildcard character is %, the proper query with LIKE would involve ‘La%’.
58. Explain ACID rule of thumb for transactions.
    Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).
59. What connections does Microsoft SQL Server support?
    Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
60. Which one is trusted and which one is untrusted?
    Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.
61. Why would you use untrusted verificaion?
    Web Services might use it, as well as non-Windows applications.
62. What does the parameter Initial Catalog define inside Connection String?
    The database name to connect to.
63. What’s the data provider name to connect to Access database?
    Microsoft.Access.
64. What does Dispose method do with the connection object?
    Deletes it from the memory.
65. What is a pre-requisite for connection pooling?
    Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.

C# developer interview questions

A representative of a high-tech company in United Kingdom sent this in today noting that the list was used for interviewing a C# .NET developer. Any corrections and suggestions would be forwarded to the author. I won’t disclose the name of the company, since as far as I know they might still be using this test for prospective employees. Correct answers are in green color.

1) The C# keyword .int. maps to which .NET type?

1. System.Int16

2. System.Int32

3. System.Int64

4. System.Int128

2) Which of these string definitions will prevent escaping on backslashes in C#?

1. string s = #.n Test string.;

2. string s = ..n Test string.;

3. string s = @.n Test string.;

4. string s = .n Test string.;

3) Which of these statements correctly declares a two-dimensional array in C#?

1. int[,] myArray;

2. int[][] myArray;

3. int[2] myArray;

4. System.Array[2] myArray;

4) If a method is marked as protected internal who can access it?

1. Classes that are both in the same assembly and derived from the declaring class.

2. Only methods that are in the same class as the method in question.

3. Internal methods can be only be called using reflection.

4. Classes within the same assembly, and classes derived from the declaring class.

5) What is boxing?

a) Encapsulating an object in a value type.

b) Encapsulating a copy of an object in a value type.

c) Encapsulating a value type in an object.

d) Encapsulating a copy of a value type in an object.

6) What compiler switch creates an xml file from the xml comments in the files in an assembly?

1. /text

2. /doc

3. /xml

4. /help

7) What is a satellite Assembly?

1. A peripheral assembly designed to monitor permissions requests from an application.

2. Any DLL file used by an EXE file.

3. An assembly containing localized resources for another assembly.

4. An assembly designed to alter the appearance or .skin. of an application.

8) What is a delegate?

1. A strongly typed function pointer.

2. A light weight thread or process that can call a single method.

3. A reference to an object in a different process.

4. An inter-process message channel.

9) How does assembly versioning in .NET prevent DLL Hell?

1. The runtime checks to see that only one version of an assembly is on the machine at any one time.

2. .NET allows assemblies to specify the name AND the version of any assemblies they need to run.

3. The compiler offers compile time checking for backward compatibility.

4. It doesn.t.

10) Which .Gang of Four. design pattern is shown below?

public class A {

    private A instance;

    private A() {

    }

    public
static A Instance {

        get

        {

            if ( A == null )

                A = new A();

            return instance;

        }

    }

}

1. Factory

2. Abstract Factory

3. Singleton

4. Builder

11) In the NUnit test framework, which attribute must adorn a test class in order for it to be picked up by the NUnit GUI?

1. TestAttribute

2. TestClassAttribute

3. TestFixtureAttribute

4. NUnitTestClassAttribute

12) Which of the following operations can you NOT perform on an ADO.NET DataSet?

1. A DataSet can be synchronised with the database.

2. A DataSet can be synchronised with a RecordSet.

3. A DataSet can be converted to XML.

4. You can infer the schema from a DataSet.

13) In Object Oriented Programming, how would you describe encapsulation?

1. The conversion of one type of object to another.

2. The runtime resolution of method calls.

3. The exposition of data.

4. The separation of interface and implementation.

ASP.NET Interview Questions and answers

his is a list of questions I have gathered and created over a period of time from my experience, many of which I felt where incomplete or simply wrong.  I have finally taken the time to go through each question and correct them to the best of my ability.  However, please feel free to post feedback to challenge, improve, or suggest new questions.  I want to thank those of you that have contributed quality questions and corrections thus far.

There are some questions in this list that I do not consider to be good questions for an interview.  However, they do exist on other lists available on the Internet so I felt compelled to keep them here for easy access.

1. Describe the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe in the page loading process.
   inetinfo.exe is theMicrosoft IIS server running, handling ASP.NET requests among other things.When an ASP.NET request is received (usually a file with .aspx extension), the ISAPI filter aspnet_isapi.dll takes care of it by passing the request tothe actual worker process aspnet_wp.exe.
    
2. What’s the difference between Response.Write() andResponse.Output.Write()?
   Response.Output.Write() allows you to write formatted output.  
3. What methods are fired during the page load?
   Init() - when the page is instantiated
   Load() - when the page is loaded into server memory
   PreRender() - the brief moment before the page is displayed to the user as HTML
   Unload() - when page finishes loading.  
4. When during the page processing cycle is ViewState available?
   After the Init() and before the Page_Load(), or OnLoad() for a control.  
5. What namespace does the Web page belong in the .NET Framework class hierarchy?
   System.Web.UI.Page  
6. Where do you store the information about the user’s locale?
   System.Web.UI.Page.Culture  
7. What’s the difference between Codebehind="MyCode.aspx.cs" andSrc="MyCode.aspx.cs"?
   CodeBehind is relevant to Visual Studio.NET only.  
8. What’s a bubbled event?
   When you have a complex control, like DataGrid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid event handler to take care of its constituents.  
9. Suppose you want a certain ASP.NET function executed on MouseOver for a certain button.  Where do you add an event handler?
   Add an OnMouseOver attribute to the button.  Example: btnSubmit.Attributes.Add("onmouseover","someClientCodeHere();");  
10. What data types do the RangeValidator control support?
    Integer, String, and Date.  
11. Explain the differences between Server-side and Client-side code?
    Server-side code executes on the server.  Client-side code executes in the client's browser.  
12. What type of code (server or client) is found in a Code-Behind class?
    The answer is server-side code since code-behind is executed on the server.  However, during the code-behind's execution on the server, it can render client-side code such as JavaScript to be processed in the clients browser.  But just to be clear, code-behind executes on the server, thus making it server-side code.  
13. Should user input data validation occur server-side or client-side?  Why?
    All user input data validation should occur on the server at a minimum.  Additionally, client-side validation can be performed where deemed appropriate and feasable to provide a richer, more responsive experience for the user.  
14. What is the difference between Server.Transfer and Response.Redirect?  Why would I choose one over the other?
    Server.Transfer transfers page processing from one page directly to the next page without making a round-trip back to the client's browser.  This provides a faster response with a little less overhead on the server.  Server.Transfer does not update the clients url history list or current url.  Response.Redirect is used to redirect the user's browser to another page or site.  This performas a trip back to the client where the client's browser is redirected to the new page.  The user's browser history list is updated to reflect the new address.  
15. Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?
    Valid answers are:
    ·  A DataSet can represent an entire relational database in memory, complete with tables, relations, and views.
    ·  A DataSet is designed to work without any continuing connection to the original data source.
    ·  Data in a DataSet is bulk-loaded, rather than being loaded on demand.
    ·  There's no concept of cursor types in a DataSet.
    ·  DataSets have no current record pointer You can use For Each loops to move through the data.
    ·  You can store many edits in a DataSet, and write them to the original data source in a single operation.
    ·  Though the DataSet is universal, other objects in ADO.NET come in different versions for different data sources. 
     
16. What is the Global.asax used for?
    The Global.asax (including the Global.asax.cs file) is used to implement application and session level events.  
17. What are the Application_Start and Session_Start subroutines used for?
    This is where you can set the specific variables for the Application and Session objects.  
18. Can you explain what inheritance is and an example of when you might use it?
    When you want to inherit (use the functionality of) another class.  Example: With a base class named Employee, a Manager class could be derived from the Employee base class.  
19. Whats an assembly?
    Assemblies are the building blocks of the .NET framework. Overview of assemblies from MSDN  
20. Describe the difference between inline and code behind.
    Inline code written along side the html in a page. Code-behind is code written in a separate file and referenced by the .aspx page.  
21. Explain what a diffgram is, and a good use for one?
    The DiffGram is one of the two XML formats that you can use to render DataSet object contents to XML.  A good use is reading database data to an XML file to be sent to a Web Service.  
22. Whats MSIL, and why should my developers need an appreciation of it if at all?
    MSIL is the Microsoft Intermediate Language. All .NET compatible languages will get converted to MSIL.  MSIL also allows the .NET Framework to JIT compile the assembly on the installed computer.  
23. Which method do you invoke on the DataAdapter control to load your generated dataset with data?
    The Fill() method.  
24. Can you edit data in the Repeater control?
    No, it just reads the information from its data source.  
25. Which template must you provide, in order to display data in a Repeater control?
    ItemTemplate.  
26. How can you provide an alternating color scheme in a Repeater control?
    Use the AlternatingItemTemplate.  
27. What property must you set, and what method must you call in your code, in order to bind the data from a data source to the Repeater control?
    You must set the DataSource property and call the DataBind method.  
28. What base class do all Web Forms inherit from?
    The Page class.  
29. Name two properties common in every validation control?
    ControlToValidate property and Text property.  
30. Which property on a Combo Box do you set with a column name, prior to setting the DataSource, to display data in the combo box?
    DataTextField property.  
31. Which control would you use if you needed to make sure the values in two different controls matched?
    CompareValidator control.  
32. How many classes can a single .NET DLL contain?
    It can contain many classes. 

Web Service Questions

1. What is the transport protocol you use to call a Web service?
   SOAP (Simple Object Access Protocol) is the preferred protocol.  
2. True or False: A Web service can only be written in .NET?
   False 
    
3. What does WSDL stand for?
   Web Services Description Language.  
4. Where on the Internet would you look for Web services?
   http://www.uddi.org  
5. True or False: To test a Web service you must create a Windows application or Web application to consume this service?
   False, the web service comes with a test page and it provides HTTP-GET method to test.
    

State Management Questions

1. What is ViewState?
   ViewState allows the state of objects (serializable) to be stored in a hidden field on the page.  ViewState is transported to the client and back to the server, and is not stored on the server or any other external source.  ViewState is used the retain the state of server-side objects between postabacks.  
2. What is the lifespan for items stored in ViewState?
   Item stored in ViewState exist for the life of the current page.  This includes postbacks (to the same page).  
3. What does the "EnableViewState" property do?  Why would I want it on or off?
   It allows the page to save the users input on a form across postbacks.  It saves the server-side values for a given control into ViewState, which is stored as a hidden value on the page before sending the page to the clients browser.  When the page is posted back to the server the server control is recreated with the state stored in viewstate.  
4. What are the different types of Session state management options available with ASP.NET?
   ASP.NET provides In-Process and Out-of-Process state management.  In-Process stores the session in memory on the web server.  This requires the a "sticky-server" (or no load-balancing) so that the user is always reconnected to the same web server.  Out-of-Process Session state management stores data in an external data source.  The external data source may be either a SQL Server or a State Server service.  Out-of-Process state management requires that all objects stored in session are serializable.

How to Use the Preview Scripts in ajax 4.0

This preview consists of release and debug versions of the following script resources:

· An updated version of MicrosoftAjax.js

· MicrosoftAjaxTemplates.js

· MicrosoftAjaxAdoNet.js

· MicrosoftAjaxDataContext.js

· An updated version of MicrosoftAjaxWebForms.js

To use the new features in a Web page, enable the updated version of Microsoft Ajax on the page. This is done either by including a <script> tag that references MicrosoftAjax.js (or MicrosoftAjax.debug.js), or by including a server-side ScriptManager control in the page under which you add a ScriptReference to the new MicrosoftAjax.js.

Then, simply include the new script files:

· MicrosoftAjaxTemplates.js (or MicrosoftAjaxTemplates.debug.js)

· MicrosoftAjaxAdoNet.js (or MicrosoftAjaxAdoNet.debug.js).

· MicrosoftAjaxDataContext.js (or MicrosoftAjaxDataContext.debug.js).

by adding corresponding ScriptReferences (under the ScriptManager control) or <script> tags.

Example using Script Manager:

<asp:ScriptManager ID="sm" runat="server">

<Scripts>

<asp:ScriptReference Name="MicrosoftAjax.js" Path="~/scripts/MicrosoftAjax.js" />

<asp:ScriptReference ScriptMode="Inherit" Path="~/scripts/MicrosoftAjaxTemplates.js" />

<asp:ScriptReference ScriptMode="Inherit" Path="~/scripts/MicrosoftAjaxAdoNet.js" />

<asp:ScriptReference ScriptMode="Inherit" Path="~/scripts/MicrosoftAjaxDataContext.js" />

</Scripts>

</asp:ScriptManager>

Example using <script> tags:

<script type="text/javascript" src="../scripts/MicrosoftAjax.debug.js"></script>

<script type="text/javascript" src="../scripts/MicrosoftAjaxTemplates.debug.js"></script>

<script type="text/javascript" src="../scripts/MicrosoftAjaxAdoNet.debug.js"></script>

<script type="text/javascript" src="../scripts/MicrosoftAjaxDataContext.debug.js"></script>

If you wish to use UpdatePanel, you will need to also include the updated version of MicrosoftAjaxWebForms.js in your page. An example of this is provided in the “UpdatePanel Support” section of this document.