Tuesday, 9 November 2010

C# Interview Question And Answers

1. Does C# support multiple-inheritance?

2. Who is a protected class-level variable available to?
It is available to any sub-class (a class inheriting this class).

3. Are private class-level variables inherited?
Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they are inherited.

4. Describe the accessibility modifier “protected internal”.
It is available to classes that are within the same assembly and derived from the specified base class.

5. What’s the top .NET class that everything is derived from?

6. What does the term immutable mean?
The data value may not be changed. Note: The variable value may be changed, but the original immutable data value was discarded and a new data value was created in memory.

7. What’s the difference between System.String and System.Text.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.

8. What’s the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each time a string is changed, a new instance in memory is created.

9. Can you store multiple data types in System.Array?

10. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The Clone() method returns a new array (a shallow copy) object containing all the elements in the original array. The CopyTo() method copies the elements into another existing array. Both perform a shallow copy. A shallow copy means the contents (each array element) contains references to the same object as the elements in the original array. A deep copy (which neither of these methods performs) would create a new instance of each element’s object, resulting in a different, yet identacle object.

11. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.

12. What’s the .NET collection class that allows an element to be accessed using a unique key?

13. What class is underneath the SortedList class?
A sorted HashTable.

14. Will the finally block get executed if an exception has not occurred?¬

15. What’s the C# syntax to catch 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 {}.

16. Can multiple catch blocks be executed for a single try statement?
No. Once the proper catch block processed, control is transferred to the finally block (if there are any).

17. Explain the three services model commonly know as a three-tier application.
Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources).

Class Questions
1. What is the syntax to inherit from a class in C#?
Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass

2. Can you prevent your class from being inherited by another class?
Yes. The keyword “sealed” will prevent the class from being inherited.

3. Can you allow a class to be inherited, but prevent the method from being over-ridden?
Yes. Just leave the class public and make the method sealed.

4. What’s an abstract class?
A class that cannot be instantiated. An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation.

5. When do you absolutely have to declare a class as abstract?
1. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
2. When at least one of the methods in the class is abstract.

6. What is an interface class?
Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes.

7. Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public, and are therefore public by default.

8. Can you inherit multiple interfaces?
Yes. .NET does support multiple interfaces.

9. What happens if you inherit multiple interfaces and 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.
To Do: Investigate

10. What’s the difference between an interface and abstract class?
In an interface class, all methods are abstract – there is no implementation. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed. An abstract class may have accessibility modifiers.

11. What is the difference between a Struct and a Class?
Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval. Another difference is that structs cannot inherit.

Method and Property Questions
1. What’s the implicit name of the parameter that gets passed into the set method/property of a class?
Value. The data type of the value parameter is defined by whatever data type the property is declared as.

2. What does the keyword “virtual” declare for a method or property?
The method or property can be overridden.

3. How is method overriding different from method overloading?
When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same name within the class.

4. Can you declare an override method to be static if the original method is not static?
No. The signature of the virtual method must remain the same. (Note: Only the keyword virtual is changed to keyword override)

5. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters.

6. If a base class has a number of overloaded constructors, and an inheriting class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific 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.

Events and Delegates
1. What’s a delegate?
A delegate object encapsulates a reference to a method.

2. What’s a multicast delegate?
A delegate that has multiple handlers assigned to it. Each assigned handler (method) is called.

XML Documentation Questions
1. Is XML case-sensitive?

2. What’s the difference between // comments, /* */ comments and /// comments?
Single-line comments, multi-line comments, and XML documentation comments.

3. How do you generate documentation from the C# file commented properly with a command-line compiler?
Compile it with the /doc switch.

Debugging and Testing Questions
1. What debugging tools come with the .NET SDK?
1. CorDBG – command-line debugger. To use CorDbg, you must compile the original C# file using the /debug switch.
2. DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR.

2. What does assert() method 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.

3. 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.

4. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose. For applications that are constantly running you run the risk of overloading the machine and the hard drive. Five levels range from None to Verbose, allowing you to fine-tune the tracing activities.

5. Where is the output of TextWriterTraceListener redirected?
To the Console or a text file depending on the parameter passed to the constructor.

6. How do you debug an ASP.NET Web application?
Attach the aspnet_wp.exe process to the DbgClr debugger.

7. What are three test cases you should go through in unit testing?
1. Positive test cases (correct data, correct output).
2. Negative test cases (broken or missing data, proper handling).
3. Exception test cases (exceptions are thrown and caught properly).

8. 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.

ADO.NET and Database Questions
1. What is the role of the DataReader class in ADO.NET connections?
It returns a read-only, forward-only rowset from the data source. A DataReader provides fast access when a forward-only sequential read is needed.

2. 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. OLE-DB.NET is a .NET layer on top of the OLE layer, so it’s not as fastest and efficient as SqlServer.NET.

3. 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%’.

4. Explain ACID rule of thumb for transactions.
A transaction must be:
1. Atomic – it is one unit of work and does not dependent on previous and following transactions.
2. Consistent – data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t.
3. Isolated – no transaction sees the intermediate results of the current transaction).
4. Durable – the values persist if the data had been committed even if the system crashes right after.

5. What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and password).

6. Between Windows Authentication and SQL Server Authentication, 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.

7. What does the Initial Catalog parameter define in the connection string?
The database name to connect to.

8. What does the Dispose method do with the connection object?
Deletes it from the memory.
To Do: answer better. The current answer is not entirely correct.

9. 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. The connection string must be identical.

Assembly Questions
1. How is 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.

2. What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.

3. What is 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.

4. What namespaces are necessary to create a localized application?
System.Globalization and System.Resources.

5. What is the smallest unit of execution in .NET?
an Assembly.

6. When should you call the garbage collector in .NET?
As a good rule, you should not call the garbage collector. However, you could call the garbage collector when you are done using a large object (or set of objects) to force the garbage collector to dispose of those very large objects from memory. However, this is usually not a good practice.

7. How do you convert a value-type to a reference-type?
Use Boxing.

8. What happens in memory when you Box and Unbox a value-type?
Boxing converts a value-type to a reference-type, thus storing the object on the heap. Unboxing converts a reference-type to a value-type, thus storing the value on the stack.

1. Explain the differences between Server-side and Client-side code?

ANS: Server side code will execute at server end all the business logic will execute at server end where as client side code will execute at client side at browser end.

2. What type of code (server or client) is found in a Code-Behind class?

ANS : Server side.

3. Should validation (did the user enter a real date) occur server-side or client-side? Why?

ANS : client side . there is no need to go to validate user input. If it relates to data base validation we need to validate at server side.

4. What does the “EnableViewState” property do? Why would I want it on or off?

ANS: IT keeps the data of the control during post backs.
if we turn off the values should not populate during server round trip.

5. What is the difference between Server.Transfer and
Response.Redirect? Why would I choose one over the other?

ANS: Server.Trnasfer will prevent round trip. it will redirect pages which or in the same directory. NO way to pass the query strings . Thru http context we can able to get the previous page control values.

Response.Redirect : There is a round trip to process the request. We can redirect to any page external / internal other than aspx. We can pass the query string thru which we can manage sessions.

6. Can you give an example of when it would be appropriate to use a web service as opposed to a non-serviced .NET component

ANS : Web services are best suite for Hetrogenious environment.
Remoting is best suite for Homogenious environment. The systems that under CLR.

7. Let’s say I have an existing application written using Visual Studio 6 (VB 6, InterDev 6) and this application utilizes Windows 2000 COM+ transaction services. How would you approach migrating this
application to .NET

We need to have Wrapper to communicate COM components in .net. and vis versa

CCW : Com Callable wrapper.
RCW : RUN time callable wrapper.

8. Can you explain the difference between an ADO.NET Dataset and anADO Recordset?\
ANS : DIsconnected architechure . Maintainace relation schemas. MUtilple table grouping.
Connected one .
9. Can you give an example of what might be best suited to place in the Application_Start and Session_Start subroutines?

ANS: APplication_start need for global variable which are available over the application.
Sesssion_Start : login dependent ( user dependent)

10. If I’m developing an application that must accomodate multiple security levels though secure login and my ASP.NET web appplication is
spanned across three web-servers (using round-robbin load balancing)
what would be the best approach to maintain login-in state for the

ANS : Database Support.
or Thru state service.

11. What are ASP.NET Web Forms? How is this technology different than what is available though ASP (1.0-3.0)?
ANS : ASP . Interprepter.. use the script engine.
ASP.Net Compiled.

12. How does VB.NET/C# achieve polymorphism?
ANS : Function overloading.
Operator overloading.
11. Can you explain what inheritance is and an example of when you might use it?

ANS : Heridity.
Use the existing functionality along with its own properities.

13. How would you implement inheritance using VB.NET/C#?
ANS: Derived Class : Basecalss
VB.NEt : Derived Class Inherits Baseclass
14. Whats an assembly
ANS : A Basic unit of executable code >

Which contains : Manifest – Meta data
versioning , Calture , IL, Reference

15. Describe the difference between inline and code behind – which is best in a loosely coupled solution

Tightly coupled – INLINE
ANS: inline function bind at compile time can write in aspx page with in <% %> .

17. Explain what a diffgram is, and a good use for one

ANS : is an xml grammer. it talk about state of node in xml file.

18. Where would you use an iHTTPModule, and what are the limitations of any approach you might take in implementing one

ANS: Preprocessing before going to IIS.

20. What are the disadvantages of viewstate/what are the benefits
ANS : IT can be hacked . page is size is heavy.

21 Describe session handling in a webfarm, how does it work and what are the limits

Session – mode
State sever

22. How would you get ASP.NET running in Apache web servers – why would you even do this?

ANS: —- Install Mod_AspDotNet
Add at the end of C:\Program Files\Apache Group\Apache2\conf\httpd.conf the following lines

23. Whats MSIL, and why should my developers need an appreciation of it if at all?

ANS : Microsoft Intermeidate lanaguage. which is the out put for all the .net supported languages after comiplation will produce.
Appreciation for cross language support.

24. In what order do the events of an ASPX page execute. As a developer is it important to undertsand these events?
ANS : INIT, PageLoad, Prerender , UNload.

25. Which method do you invoke on the DataAdapter control to load your generated dataset with data?


26. Can you edit data in the Repeater control?

27. Which template must you provide, in order to display data in a Repeater control?

28. How can you provide an alternating color scheme in a Repeatercontrol?


29. What property must you set, and what method must you call in your code, in order to bind the data from some data source to the Repeatercontrol?


30. What base class do all Web Forms inherit from?


31. What method do you use to explicitly kill a user s session?


32 How do you turn off cookies for one page in your site?

33. Which two properties are on every validation control?
control to validate, error message
34. What tags do you need to add within the asp:datagrid tags to bind
columns manually?
autogenerated columns is set to false
35. How do you create a permanent cookie?
Cooke = ne cookee().

36. What tag do you use to add a hyperlink column to the DataGrid?
hyper link column

37. What is the standard you use to wrap up a call to a Web service
38. Which method do you use to redirect the user to another page without performing a round trip to the client?
39. What is the transport protocol you use to call a Web service SOAP
40. True or False: A Web service can only be written in .NET
41. What does WSDL stand for? webservice discription language. it is used to generate for proxy( server object)

42. What property do you have to set to tell the grid which page to go to when using the Pager object?
Page Index.

43. Where on the Internet would you look for Web services?
44. What tags do you need to add within the asp:datagrid tags to bind columns manually.

Autogenerate columns

45. 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?


46. How is a property designated as read-only?
47. Which control would you use if you needed to make sure the values in two different controls matched?
compare filed validator

48. True or False: To test a Web service you must create a windows application or Web application to consume this service?
49. How many classes can a single .NET DLL contain?

as many as u want..

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