C# Interview Questions

General Questions:

1. Does C# support multiple-inheritance?
   No.
    
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?
   System.Object.
    
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?
   No.
    
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?
    HashTable.
     
13. What class is underneath the SortedList class?
    A sorted HashTable.
     
14. Will the finally block get executed if an exception has not occurred?­
    Yes.
     
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 {}.
     

What's the difference between a programming language, a scripting language?

What's the difference between a programming language, a scripting language?

The main difference between a "programming language" (C, C++ etc.) and a "scripting language" (ASP, JSP, JavaScript, VBScript) is that code written in a programming language needs to be compiled before it is run. Once it is compiled, it can be run any number of times. Scripting languages, on the other hand, are interpreted at run-time. This means that every time you want to run the program, a separate program needs to read the code, interpret it, and then follow the instructions in the code. Compiled code has already been interpreted into machine language, so it is will typically execute faster because the conversion into machine language has already been done. --Vanesh.

ASP.NET Interview Questions

1.	Difference between thread and process?
	Thread - is used to execute more than one program at a time. process - executes single program
2.	Explain Namespace.
	Namespaces are logical groupings of names used within a program. There may be multiple namespaces in a single application code, grouped based on the identifiers’ use. The name of any given identifier must appear only once in its namespace.
3.	List the types of Authentication supported by ASP.NET.
	Windows (default) Forms Passport None (Security disabled)
4.	What is CLR?
	Common Language Runtime (CLR) is a run-time environment that manages the execution of .NET code and provides services like memory management, debugging, security, etc. The CLR is also known as Virtual Execution System (VES).
5.	What is CLI?
	The CLI is a set of specifications for a runtime environment, including a common type system, base class library, and a machine-independent intermediate code known as the Common Intermediate Language (CIL).
6.	List the various stages of Page-Load lifecycle.
	o Init() o Load() o PreRender() o Unload()
7.	Explain Assembly and Manifest.
	An assembly is a collection of one or more files and one of them (DLL or EXE) contains a special metadata called Assembly Manifest. The manifest is stored as binary data and contains details like versioning requirements for the assembly, the author, security permissions, and list of files forming the assembly. An assembly is created whenever a DLL is built. The manifest can be viewed programmatically by making use of classes from the System.Reflection namespace. The tool Intermediate Language Disassembler (ILDASM) can be used for this purpose. It can be launched from the command prompt or via Start> Run.
8.	What is Shadow Copy?
	In order to replace a COM component on a live web server, it was necessary to stop the entire website, copy the new files and then restart the website. This is not feasible for the web servers that need to be always running. .NET components are different. They can be overwritten at any time using a mechanism called Shadow Copy. It prevents the Portable Executable (PE) files like DLLs and EXEs from being locked. Whenever new versions of the PEs are released, they are automatically detected by the CLR and the changed components will be automatically loaded. They will be used to process all new requests not currently executing, while the older version still runs the currently executing requests. By bleeding out the older version, the update is completed.
9.	What is DLL Hell?
	DLL hell is the problem that occurs when an installation of a newer application might break or hinder other applications as newer DLLs are copied into the system and the older applications do not support or are not compatible with them. .NET overcomes this problem by supporting multiple versions of an assembly at any given time. This is also called side-by-side component versioning.
10.	Explain Web Services.
	Web services are programmable business logic components that provide access to functionality through the Internet. Standard protocols like HTTP can be used to access them. Web services are based on the Simple Object Access Protocol (SOAP), which is an application of XML. Web services are given the .asmx extension.
11.	Explain Windows Forms.
	Windows Forms is employed for developing Windows GUI applications. It is a class library that gives developers access to Windows Common Controls with rich functionality. It is a common GUI library for all the languages supported by the .NET Framework.
12.	What is Postback?
	When an action occurs (like button click), the page containing all the controls within the <FORM... > tag performs an HTTP POST, while having itself as the target URL. This is called Postback.
13.	Explain the differences between server-side and client-side code?
	Server side scripting means that all the script will be executed by the server and interpreted as needed. Client side scripting means that the script will be executed immediately in the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in VBScript or JavaScript. Since the code is included in the HTML page, anyone can see the code by viewing the page source. It also poses as a possible security hazard for the client computer.
14.	Enumerate the types of Directives.
	@ Page directive @ Import directive @ Implements directive @ Register directive @ Assembly directive @ OutputCache directive @ Reference directive
15.	What is Code-Behind?
	Code-Behind is a concept where the contents of a page are in one file and the server-side code is in another. This allows different people to work on the same page at the same time and also allows either part of the page to be easily redesigned, with no changes required in the other. An Inherits attribute is added to the @ Page directive to specify the location of the Code-Behind file to the ASP.NET page.
16.	Describe the difference between inline and code behind.
	Inline code is written along side the HTML in a page. There is no separate distinction between design code and logic code. Code-behind is code written in a separate file and referenced by the .aspx page.
17.	List the ASP.NET validation controls?
	RequiredFieldValidator RangeValidator CompareValidator RegularExpressionValidator CustomValidator ValidationSummary
18.	What is Data Binding?
	Data binding is a way used to connect values from a collection of data (e.g. DataSet) to the controls on a web form. The values from the dataset are automatically displayed in the controls without having to write separate code to display them.
19.	Describe Paging in ASP.NET.
	The DataGrid control in ASP.NET enables easy paging of the data. The AllowPaging property of the DataGrid can be set to True to perform paging. ASP.NET automatically performs paging and provides the hyperlinks to the other pages in different styles, based on the property that has been set for PagerStyle.Mode.
20.	Should user input data validation occur server-side or client-side? Why?
	All user input data validation should occur on the server and minimally on the client-side, though it is a good way to reduce server load and network traffic because we can ensure that only data of the appropriate type is submitted from the form. It is totally insecure. The user can view the code used for validation and create a workaround for it. Secondly, the URL of the page that handles the data is freely visible in the original form page. This will allow unscrupulous users to send data from their own forms to your application. Client-side validation can sometimes be performed where deemed appropriate and feasible to provide a richer, more responsive experience for the user.
21.	What is the difference between Server.Transfer and Response.Redirect?
	* Response. Redirect: This tells the browser that the requested page can be found at a new location. The browser then initiates another request to the new page loading its contents in the browser. This results in two requests by the browser. * Server. Transfer: It transfers execution from the first page to the second page on the server. As far as the browser client is concerned, it made one request and the initial page is the one responding with content. The benefit of this approach is one less round trip to the server from the client browser. Also, any posted form variables and query string parameters are available to the second page as well.
22.	What is an interface and what is an abstract class?
	In an interface, all methods must be abstract (must not be defined). In an abstract class, some methods can be defined. In an interface, no accessibility modifiers are allowed, whereas it is allowed in abstract classes.
23.	Session state vs. View state:
	In some cases, using view state is not feasible. The alternative for view state is session state. Session state is employed under the following situations: o Large amounts of data - View state tends to increase the size of both the HTML page sent to the browser and the size of form posted back. Hence session state is used. o Secure data - Though the view state data is encoded and may be encrypted, it is better and secure if no sensitive data is sent to the client. Thus, session state is a more secure option. o Problems in serializing of objects into view state - View state is efficient for a small set of data. Other types like DataSet are slower and can generate a very large view state.
24.	Can two different programming languages be mixed in a single ASPX file?
	ASP.NET’s built-in parsers are used to remove code from ASPX files and create temporary files. Each parser understands only one language. Therefore mixing of languages in a single ASPX file is not possible.
25.	Is it possible to see the code that ASP.NET generates from an ASPX file?
	By enabling debugging using a <%@ Page Debug="true" %> directive in the ASPX file or a <compilation debug="true"> statement in Web.config, the generated code can be viewed. The code is stored in a CS or VB file (usually in the \%SystemRoot%\Microsoft.NET\Framework\v1.0.nnnn\Temporary ASP.NET Files).
26.	Can a custom .NET data type be used in a Web form?
	This can be achieved by placing the DLL containing the custom data type in the application root's bin directory and ASP.NET will automatically load the DLL when the type is referenced.
27.	List the event handlers that can be included in Global.asax?
	o Application start and end event handlers o Session start and end event handlers o Per-request event handlers o Non-deterministic event handlers
28.	Can the view state be protected from tampering?
	This can be achieved by including an @ Page directive with an EnableViewStateMac="true" attribute in each ASPX file that has to be protected. Another way is to include the <pages enableViewStateMac="true" /> statement in the Web.config file.
29.	Can the view state be encrypted?
	The view state can be encrypted by setting EnableViewStateMac to true and either modifying the <machineKey> element in Machine.config to <machineKey validation="3DES” /> or by adding the above statement to Web.config.
30.	When during the page processing cycle is ViewState available?
	The view state is available after the Init() and before the Render() methods are called during Page load.