C# interview question and ANS

  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.

  Can you store multiple data types in System.Array? No.

  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.

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

  What’s the .NET datatype that allows the retrieval of data by a unique key? HashTable.

  What’s class SortedList underneath? A sorted HashTable.

  Will finally block get executed if the exception had not occurred? Yes.

  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 {}.

  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.

  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.

  What’s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.

  What’s a multicast delegate? It’s a delegate that points to and eventually fires off several methods.

  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.

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

  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.

  What namespaces are necessary to create a localized application? System.Globalization, System.Resources.

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

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

  What’s the difference between <c> and <code> XML documentation tag? Single line code example and multiple-line code example.

  Is XML case-sensitive? Yes, so <Student> and <student> are different elements.

  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.

  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.

  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.

  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 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.

  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? 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).

  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.

  Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).

  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.

  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.

  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%’.

  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).

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

  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.

  Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications.

  What does the parameter Initial Catalog define inside Connection String? The database name to connect to.

  What’s the data provider name to connect to Access database? Microsoft.Access.

  What does Dispose method do with the connection object? Deletes it from the memory.

  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.

1.	What is C#?
	C# (pronounced "C sharp") is a simple, modern, object-oriented, and type-safe programming language. It will immediately be familiar to C and C++ programmers. C# combines the high productivity of Rapid Application Development (RAD) languages.

2.	What are the types of comment in C#?
	There are 3 types of comments in C#. Single line (//) Multi (/* */) Page/XML Comments (///).

3.	What are the namespaces used in C#.NET?
	Namespace is a logical grouping of class. using System; using System.Collections.Generic; using System.Windows.Forms;

4.	What are the characteristics of C#?
	There are several characteristics of C# are : Simple Type safe Flexible Object oriented Compatible Consistent Interoperable Modern

5.	How does C# differ from C++?
	C# does not support #include statement. It uses only using statement. In C# , class definition does not use a semicolon at the end. C# does not support multiple code inheritance. Casting in C# is much safer than in c++. In C# switch can also be used on string values. Command line parameters array behave differently in C# as compared to C++.

1. What is ASP?

Active Server Pages (ASP), also known as Classic ASP, is a Microsoft's server-side technology, which helps in creating dynamic and user-friendly Web pages. It uses different scripting languages to create dynamic Web pages, which can be run on any type of browser. The Web pages are built by using either VBScript or JavaScript and these Web pages have access to the same services as Windows application, including ADO (ActiveX Data Objects) for database access, SMTP (Simple Mail Transfer Protocol) for e-mail, and the entire COM (Component Object Model) structure used in the Windows environment. ASP is implemented through a dynamic-link library (asp.dll) that is called by the IIS server when a Web page is requested from the server.

2. What is ASP.NET?

ASP.NET is a specification developed by Microsoft to create dynamic Web applications, Web sites, and Web services. It is a part of .NET Framework. You can create ASP.NET applications in most of the .NET compatible languages, such as Visual Basic, C#, and J#. The ASP.NET compiles the Web pages and provides much better performance than scripting languages, such as VBScript. The Web Forms support to create powerful forms-based Web pages. You can use ASP.NET Web server controls to create interactive Web applications. With the help of Web server controls, you can easily create a Web application.

3. What is the basic difference between ASP and ASP.NET?

The basic difference between ASP and ASP.NET is that ASP is interpreted; whereas, ASP.NET is compiled. This implies that since ASP uses VBScript; therefore, when an ASP page is executed, it is interpreted. On the other hand, ASP.NET uses .NET languages, such as C# and VB.NET, which are compiled to Microsoft Intermediate Language (MSIL).

4. In which event are the controls fully loaded?

Page load event guarantees that all controls are fully loaded. Controls are also accessed in Page_Init events but you will see that view state is not fully loaded during this event

5. How can we identify that the Page is Post Back?

Page object has an "IsPostBack" property, which can be checked to know that is the page posted back.

6. What is the lifespan for items stored in ViewState?

The items stored in ViewState live until the lifetime of the current page expires including the postbacks to the same page.