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C# Programming Language
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Intro ------------------------------
Microsoft .NET allows to use more than 30 supported programming languages which can easily inter-operate.
C#, C++, Visual Basic, etc (~ 30 languages) =>.NET Class Libraries => MSIL (Microsoft Intermediate Language == similar to Java byte code) => CLR (Common Language Runtime == similar to Java virtual machine) => Machine Native Processor
Learning C#:
Note: C# is very similar to Java. So if you know Java - it translates almost one-to-one into C# with some small changes (writeln => Writeln, import => using, etc.).
C# developers can use many powerful enhancements and development tools, for example:
Visual Studio 2010 comes with .NET 4.0 which has some new exciting features. View this video on youtube:
C# 4.0- With Anders Hejlsberg, Mads Torgersen, and Eric Lippert
- http://www.youtube.com/watch?v=KzSY9WQXjzg
- http://www.youtube.com/watch?v=s0_mvBU5HL4
New features:
Task Parallel Library (TPL) - simple syntax to invoke parallel execution using the word "Parallel".
It is much simpler than creating threads yourself, for example:
Parallel.ForEach (arr, (string item) => {
// Do something
});
Parallel.ForEach (arr, item => {
// Do something
});
Parallel.For(0, height, y => {
for (int x = 0; x < width; x++) {
ProcessPixel(x, y);
}
}
PLINQ = parallel LINQ
New graphical interface in MS VS 2010 which shows threads in the debugger. Each thread group is shown as a tree of boxes, you can see states of individual threads as you click through the steps in the debugger. You can temporarily connect the debugger to a process running on another computer to explore the threads.
The new 2010 development tools are quite amazing.
Types of applications:
Console Application | to invoke from prompt in CMD window |
Windows Forms | older way to create GUI applications using .NET |
WPF | Windows Presentation Foundation (.NET 4) - newer preferred way to create GUI applications - http://windowsclient.net/ |
ASP.NET | web pages = Web Forms. |
Silverlight | small subset of .NET Framework running in its own runtime engine (plugin in the browser) |
WCF Service Application | WCF = Windows Communication Foundation - framework for messaging (request/reply, duplex exchange, etc.). Supports metadata standards (WSDL, XML Schema and WS-Policy). Most common is to send text encoded SOAP messages via HTTP. Alternatively, WCF allows you to send messages over TCP, named pipes, or MSMQ. WCF supports transactions. |
First "Hello World" program
// Hello World program - in file Hello2.cs using System; public class Hello2 { public static void Main() { Console.WriteLine("Hello, World!"); } } |
Getting command-line parameters:
// getting command line arguments using System; public class Hello3 { public static void Main(string[] args) { Console.WriteLine("Hello, World!"); Console.WriteLine("You entered the following {0} command line arguments:", args.Length ); for (int i=0; i < args.Length; i++) { Console.WriteLine("{0}", args[i]); } } } |
Note:
There are 2 ways to compile your programs:
When you create a new project form inside GUI - it will ask about the type you want:
Note:
Other types of applications:
Collections
Collection | Code Example |
List | using System; using System.Collections.Generic; class Program { static void Main() { // list of integers List |
ArrayList | ArrayList ab = new ArrayList(); ab.Add("a"); //old fashioned way ab.Add("b"); ArrayList abcd = new ArrayList(); abcd.AddRange(new string[] {"a","b","c","d"}); // new method |
Dictionary | using System; using System.Collections.Generic; class Program { static void Main() { Dictionary d = new Dictionary(); d.Add("cat", 2); d.Add("dog", 1); d.Add("llama", 0); d.Add("iguana", -1); if (d.ContainsKey("apple")) // True |
Queue, Stack |
using System; using System.Collections; public class myQueue { public static void Main() { // Create and instantiate new queue Queue myQueue = new Queue(); // Adding 4 objects to the Queue myQueue.Enqueue("Vijay"); myQueue.Enqueue("Vikas"); ... |
invoking class/method by name
Reflection - similar to classByName() in Java:
// Invoking method of a class by name using System; using System.Reflection; public class InvokeDemo { static object run(string classname, string methodname) { Assembly asm = Assembly.Load(“mscorlib.dll”); Type type = asm.GetType(classname); object obj = asm.CreateInstance(classname); object[] args = new object[0]; object ret = type.InvokeMember( methodname, BindingFlags.Default | BindingFlags.InvokeMethod, null, obj, args ); return ret; } public static void Main(string[] args) { while (true) { try { Console.WriteLine(); Console.Write(“Enter class name: “); string classname = Console.ReadLine(); Console.Write(“Enter method name: “); string methodname = Console.ReadLine(); object ret = run(classname, methodname); Console.WriteLine(“ret value = “ + ret); } catch (System.Exception exc) { Console.WriteLine(“exception: “ + exc); } } } } |
Interview Questions
General Questions
Question | Answer |
Does C# support multiple-inheritance? | No, not multiple inheritance for classes. C# supports multiple interface though. |
Who is a protected class-level variable available to? | It is available to any sub-class (a class inheriting this class) |
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 |
Describe the accessibility modifier “protected internal” | It is available to classes that are within the same assembly OR derived from the specified base class |
What is the dIfference between Friend and Protected Friend? | Protected variable will be accessed in inherited class, but
instance variable of class cant access protected variable. While friend variable will be accessed in inherited class
as well as instance variable of class across the project. |
What’s the top .NET class that everything is derived from? | System.Object |
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. |
What’s the difference between System.String and System.Text.StringBuilder classes? | String is immutable. StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed. |
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. |
Can you store multiple data types in System.Array? | No. |
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. |
How can you sort the elements of the array in descending order? | By calling Sort() and then Reverse() methods. |
What’s the .NET collection class that allows an element to be accessed using a unique key? | HashTable. |
What class is underneath the SortedList class? | A sorted HashTable. Although today Dictionary is preferable to use. Dictionary<int, string> myDict = new Dictionary<int, string>(); myDict.Add(2, "This"); myDict.Add(1, "is"); myDict.Add(5, "radio"); myDict.Add(4, "clash"); List<string> song = new List<string>(myDict.Values); |
Will the finally block get executed if an exception has not occurred? | Yes |
What’s the C# syntax to catch any possible exception? | catch {} - catches everything |
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). |
What are the four different ways of passing parameters to a method in C#. | 1. Value 2. Out 3. Ref 4. Params |
What are typing categories | - Value types - store data. |
What is Boxing and Unboxing | int i = 123;
object o = i; // boxing - putting value into object |
Class Questions
Question | Answer |
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 |
Can you prevent your class from being inherited by another class? | Yes. The keyword “sealed” will prevent the class from being inherited.You CAN'T declare a method as sealed - unless it overrides the base method, for example: public override sealed void Method() { ... } . To prevent overriding of a method, don't specify the "virtual" keyword. |
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. |
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. |
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. |
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. |
Why can’t you specify the accessibility modifier for methods inside the interface? | They all must be public, and are therefore public by default. |
Can you inherit multiple interfaces? | Yes. |
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. You can do explicit implementation if you need different behavior. public class Class1 : IFoo, IFoo2, IFoo3 { public void TheMethod() {Console.Write("1");} void IFoo.TheMethod() {Console.Write("2");} void IFoo2.TheMethod() {Console.Write("3");} } Class1 myClass = new Class1(); myClass.TheMethod(); // writes out "1"; ((IFoo) myClass).TheMethod(); // writes out "2"; ((IFoo2) myClass).TheMethod(); // writes out "3"; ((IFoo3) myClass).TheMethod(); // writes out "1"; |
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. |
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
Question | Answer |
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. |
What does the keyword “virtual” declare for a method or property? | The method or property can be overridden. |
How is method overriding different from method overloading? | When overriding a method, you change the behavior of the method for the derived class. The signature of the method is the same. Overloading a method simply involves having another method with the same name but different signature (parameters number, order or types) within the class. |
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) |
What are the different ways a method can be overloaded? | Different parameter data types, different number of parameters, different order of parameters. |
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
Question | Answer |
What’s a delegate? | A delegate object encapsulates a reference to a method. Works like "type safe function pointer". |
What’s a multicast delegate? | A delegate that has multiple handlers assigned to it. Each assigned handler (method) is called. |
XML Documentation Questions
Question | Answer |
Is XML case-sensitive? | Yes |
What’s the difference between // comments, /* */ comments and /// comments? | Single-line comments, multi-line comments, and XML documentation comments. |
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
Question | Answer |
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. |
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. |
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. |
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. |
Where is the output of TextWriterTraceListener redirected? | To the Console or a text file depending on the parameter passed to the constructor. |
How do you debug an ASP.NET Web application? | Attach the aspnet_wp.exe process to the DbgClr debugger. |
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). |
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
Question | Answer |
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. |
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. |
What is the wildcard character in SQL? | %. For example, ‘La%’. |
What is ACID for transactions. | Atomic, Consistent, Isolated, Durable |
What connections does Microsoft SQL Server support? | Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and password). |
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. |
What does the Initial Catalog parameter define in the connection string? | The database name to connect to. |
What does the Dispose method do with the connection object? | Dispose is the method, which we call usually when we want the object to be garbage collected. The dispose method will release all the resources owned by the object (Finalize() method). And then it calls the dispose() of its parent class. This is probagated through the base type hierarchy. For database connection, The Dispose method closes the connection. The Dispose method and the Close method are equivalent. The first time a connection object is created, a connection pool is created. Subsequent instantiations of the connection object does not create a new connection pool (unless the connection string changes), a connection is retrieved from the pool. The connection pool remains in memory until the application exits. |
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
Question | Answer |
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. |
What are the ways to deploy an assembly? | An MSI installer, a CAB archive, and XCOPY command. |
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. |
What namespaces are necessary to create a localized application? | System.Globalization and System.Resources. |
What is the smallest unit of execution in .NET? | an Assembly. |
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. |
How do you convert a value-type to a reference-type? | Use Boxing. |
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. |
More questions:
When is CLR loaded in the memory? Is there only one instance of CLR running when we are running multiple applications? How is CLR first loaded? How is an assembly loaded in CLR and executed?
- Global Assembly Cache (GAC)
- DataSet vs. DataReader
- Remoting
- Web Service
- deployment
1. What is serialization, how it works in .NET?
2. What should one do to make class serializable?
3. What exactly is being serialized when you perform serialization?
4. scope in C#
Simply, the scope of a type (a variable, a method, or a class) is where you can use that type in your program. In other words, the scope defines the area of the program where that type can be accessible and referenced.
When you declare a variable inside a block of code (like a method or an if statement structure), it will have a local scope, and it will be called a local-variable. Local scope means that you can't refer to that variable outside that block of code.
1). If we declare a class as a private class can we inherit that class?
2). Can a declare public variables in a private class?If yes then can we access those variables?
What is reflection? Can you give me some examples of reflection?
- Difference between DataReader and DataAdapter / DataSet and DataAdapter?
1) Can we have private constructor? when can I use them? private constructors can be used when you want to control creation of instances. For example, Singleton.
2) what is an internal specifier? what happens internally when I use access specifier Internal ?
3) DO we have inline function in C#? ohterwise what is equivalent inline function in C#?
How to pass variable parameter list in c#?
using the params keyword.
There are two primary exception throwing scenarios:
- Throwing a new exception (creating and throwing it)
- Re-Throwing an exception (an exception that has been caught within a try/catch block)
1. Use of Enable view state ? if turn off what happen ?
2. Response.write,server.transfer difference which one is used when ?
3. server.transfer limitation ?
4. how can i kill user session ?
5. wild card character in sql ?
6. can aspx page contains two pager tags ?
7. can aspx page have multi language declarations ?
8. readonly syntax ?
9. which control is used to compare two controls?
10. two common propertys for any validation contro ?
11. what is an assembly ?
12. what is inheritancy where u required ?
13 polymorphism and advantage ?
14. what is the method while we are using adapter and dataset ?
15. what are the things we generally declare in session_start , application_start ?
16. .net class library to find unique key?
17. can Array contains different datatypes ?
18. ACID properties ?
19. which tag i need to use manually to bind columns in a datagrid ?
20. throw exception and rethrowing difference. ?
21. when garbage collector come into picture. ?
22. what is code behined and an aspx files are for?
23. how u maintain data while navigating one page to another
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
users?
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
ANS:
Session - mode
State sever
OUtprocess
sql
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?
Fill()
26. Can you edit data in the Repeater control?
NO
27. Which template must you provide, in order to display data in a Repeater control?
ITemtemplate
28. How can you provide an alternating color scheme in a Repeatercontrol?
AlternateItemTemplate
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?
Datasource,
DataBind
30. What base class do all Web Forms inherit from?
System.Web.UI.Page
31. What method do you use to explicitly kill a user s session?
abondon()
32 How do you turn off cookies for one page in your site?
disablecookies.
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().
cooke.adddate.
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?
server.transfer
39. What is the transport protocol you use to call a Web service SOAP
http
40. True or False: A Web service can only be written in .NET
false
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?
UDDI
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?
datatext
datavalue
46. How is a property designated as read-only?
get
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?
no
49. How many classes can a single .NET DLL contain?
as many as u want..
--> ASP.Net page lifecycle
--> What is first event of Datagrid for binding the data.
--> What is itemcreated and itemdatabound
--> What is Postback
--> What is multi file Assembly.
--> How many assemblies u will get after compiling a solution of some projects.
--> How the iis server processes a client request.
--> What are the contents of an assembly.
--> What is delay signing.
--> AppDomain vs HttpApplicationObject
================================================
1). The C# default parameterless constructor
2). The Default Static constructor provided for static objects
Code a simple app with just a basic class with one simple field. Create the assembly. Use ildasm to view the intermediate code. You will be able to see the above two points. Watch out for ctor and cctor
2). Use of Static variable in a Method in c#2.0 allowed or not? try it