Thursday, February 23, 2012

MNC Companies(HCL, Infosys, IBM, Wipro, TCS, NIIT....) Interview Questions on C# .Net

Ques:Is it possible to have a static indexer in C#?  
Sol:No. Static indexers are not allowed in C#. 

Ques:Does C# support templates?
Sol:No. However, there are plans for C# to support a type of template known as a generic. These generic types have similar syntax but are instantiated at run time as opposed to compile time. You can read more about them here.

Ques:Does C# support C type macros?
Sol:No. C# does not have macros. Keep in mind that what some of the predefined C macros (for example, __LINE__ and __FILE__) give you can also be found in .NET classes like System.Diagnostics (for example, StackTrace and StackFrame), but they'll only work on debug builds.

Ques:Can you store multiple data types in System.Array?

Ques:Is it possible to inline assembly or IL in C# code?

Ques:Can you declare the override method static while the original method is non-static?
Sol:No, you cannot, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override

Ques:Does C# support multiple inheritance?
Sol:No, use interfaces instead.

Ques:Can multiple catch blocks be executed?
Sol: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.

Ques:Can you override private virtual methods?
Sol:No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

Ques:What is a pre-requisite for connection pooling?
Sol:Multiple processes must agree that they will share the same connection, where every parameter is the same,

Ques:What is the data provider name to connect to Access database?

Ques:Why does my Windows application pop up a console window every time I run it?
Sol:Make sure that the target type set in the project properties setting is set to Windows Application, and not Console Application. If you're using the command line, compile with /target:winexe & not target:exe. 

Ques:What is the wildcard character in SQL?
Sol:Let us 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%.

Ques:What is the role of the DataReader class in ADO.NET connections?
Sol:It returns a read-only dataset from the data source when the command is executed.

Ques:What does the This window show in the debugger?
Sol:It points to the object that is pointed to by this reference. Object’s instance data is shown.

Ques:Describe the accessibility modifier protected internal?
Sol:It is available to derived classes and classes within the same Assembly (and naturally from the base class it is declared in).

Ques:What is an interface class?
Sol:It is an abstract class with public abstract methods all of which must be implemented in the inherited classes.

Ques:What is a multicast delegate?
Sol:It is a delegate that points to and eventually fires off several methods.

Ques:How does one compare strings in C#?
Sol:In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings' values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { ... } Here's an example showing how string compares work: using System;
public class StringTest
public static void Main(string[] args)
Object nullObj = null;
Object realObj = new StringTest();
int i = 10;
Console.WriteLine("Null Object is [" + nullObj + "]n" +
"Real Object is [" + realObj + "]n" +
"i is [" + i + "]n");
// Show string equality operators
string str1 = "foo";
string str2 = "bar";
string str3 = "bar";
Console.WriteLine("{0} == {1} ? {2}", str1, str2, str1 == str2 );
Console.WriteLine("{0} == {1} ? {2}", str2, str3, str2 == str3 );
Output: Null Object is []
Real Object is [StringTest]
i is [10]
foo == bar ? False
bar == bar ? True

Ques:What does assert() do?
Sol: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.

Ques:How do I get deterministic finalization in C#?
Sol:In a garbage collected environment, it's impossible to get true determinism. However, a design pattern that we recommend is implementing IDisposable on any class that contains a critical resource. Whenever this class is consumed, it may be placed in a using statement, as shown in the following example:
using(FileStream myFile = File.Open(@"c:temptest.txt",
int fileOffset = 0;
while(fileOffset < myFile.Length)
When myFile leaves the lexical scope of the using, its dispose method will be called.

Ques:How can I get around scope problems in a try/catch?
Sol:If you try to instantiate the class inside the try, it'll be out of scope when you try to access it from the catch block. A way to get around this is to do the following: Connection conn = null;
conn = new Connection();
if (conn != null) conn.Close();
By setting it to null before the try block, you avoid getting the CS0165 error (Use of possibly unassigned local variable 'conn').

Ques:Why do I get an error (CS1006) when trying to declare a method without specifying a return type?
Sol:If you leave off the return type on a method declaration, the compiler thinks you are trying to declare a constructor. So if you are trying to declare a method that returns nothing, use void. The following is an example: // This results in a CS1006 error public static staticMethod (mainStatic obj) // This will work as wanted public static void staticMethod (mainStatic obj) 

Ques:How do I convert a string to an int in C#?
Sol:Here's an example: using System;
class StringToInt
public static void Main()
String s = "105";
int x = Convert.ToInt32(s);

Ques:How do you directly call a native function exported from a DLL?
Sol:Here's a quick example of the DllImport attribute in action: using System.Runtime.InteropServices;
class C
public static extern int MessageBoxA(int h, string m, string c, int type);
public static int Main()
return MessageBoxA(0, "Hello World!", "Caption", 0);
This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation.

Ques:What is the .NET datatype that allows the retrieval of data by a unique key?

Ques:How do you specify a custom attribute for the entire assembly (rather than for a class)?
Sol:Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:
using System;
[assembly : MyAttributeClass]
class X {}
Note that in an IDE-created project, by convention, these attributes are placed in

Ques:What is the difference between a struct and a class in C#?
Sol:From language spec:
The list of similarities between classes and structs is as follows. Longstructs can implement interfaces and can have the same kinds of members as classes. Structs differ from classes in several important ways; however, structs are value types rather than reference types, and inheritance is not supported for structs. Struct values are stored on the stack or in-line. Careful programmers can sometimes enhance performance through judicious use of structs. For example, the use of a struct rather than a class for a Point can make a large difference in the number of memory allocations performed at runtime. The program below creates and initializes an array of 100 points. With Point implemented as a class, 101 separate objects are instantiated-one for the array and one each for the 100 elements.

Ques:What is the difference between the Debug class and Trace class?
Sol:Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.

Ques:How can you overload a method?
Sol:Different parameter data types, different number of parameters, different order of parameters.

Ques:What debugging tools come with the .NET SDK?
Sol: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.

Ques:What does Dispose method do with the connection object?
Sol:Deletes it from the memory.

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

Ques:When you inherit a protected class-level variable, who is it available to?
Sol:Classes in the same namespace.
Ques:Does C# support #define for defining global constants?
Sol:No. If you want to get something that works like the following C code:
#define A 1
use the following C# code: class MyConstants
public const int A = 1;
Then you use MyConstants.A where you would otherwise use the A macro.
Using MyConstants.A has the same generated code as using the literal 1.  
Ques:How can I get the ASCII code for a character in C#?
Sol:Casting the char to an int will give you the ASCII value: char c = 'f'; System.Console.WriteLine((int)c); or for a character in a string: System.Console.WriteLine((int)s[3]); The base class libraries also offer ways to do this with the Convert class or Encoding classes if you need a particular encoding.

Ques:Is there an equivalent to the instanceof operator in Visual J++?
Sol:C# has the is operator:
expr is type

Ques:How do I create a Delegate/MulticastDelegate?
Sol:C# requires only a single parameter for delegates: the method address. Unlike other languages, where the programmer must specify an object reference and the method to invoke, C# can infer both pieces of information by just specifying the method's name. For example, let's use System.Threading.ThreadStart: Foo MyFoo = new Foo(); ThreadStart del = new ThreadStart(MyFoo.Baz); This means that delegates can invoke static class methods and instance methods with the exact same syntax!

Ques:How do destructors and garbage collection work in C#?
Sol:C# has finalizers (similar to destructors except that the runtime doesn't guarantee they'll be called), and they are specified as follows:
class C
// your code
public static void Main() {}
Currently, they override object.Finalize(), which is called during the GC process.

Ques:My switch statement works differently! Why?
Sol:C# does not support an explicit fall through for case blocks.
The following code is not legal and will not compile in C#: switch(x)
case 0:
// do something
case 1:
// do something in common with 0
// do something in common with
//0, 1 and everything else
To achieve the same effect in C#, the code must be modified
as shown below (notice how the control flows are explicit): class Test
public static void Main()
int x = 3;
case 0:
// do something
goto case 1;
case 1:
// do something in common with 0
goto default;
// do something in common with 0, 1, and anything else

Ques:How can I access the registry from C# code?
Sol:By using the Registry and RegistryKey classes in Microsoft.Win32, you can easily access the registry. The following is a sample that reads a key and displays its value:
using System;using Microsoft.Win32;
class regTest
public static void Main(String[] args)
RegistryKey regKey;
Object value;
regKey = Registry.LocalMachine;
regKey =
regKey.OpenSubKey("HARDWAREDESCRIPTIONSystemCentralProcessor ");
value = regKey.GetValue("VendorIdentifier");
Console.WriteLine("The central processor of this machine is: {0}.", value);

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

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

Ques:How do you mark a method obsolete?
Sol:Assuming you've done a "using System;": [Obsolete]
public int Foo() {...}
or [Obsolete("This is a message describing why this method is obsolete")]
public int Foo() {...}
Note: The O in Obsolete is capitalized.

Ques:How is the DLL Hell problem solved in .NET?
Sol: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

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

Ques:Why does DllImport not work for me?
Sol:All methods marked with the DllImport attribute must be marked as public static extern.

Ques:What is a delegate?
Sol:A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.

Ques:What is the difference between an interface and abstract class?
Sol: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.

Ques:What is an abstract class?
Sol: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 is a blueprint for a class without any implementation.

Ques:Does C# support multiple-inheritance?

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

Ques:Can you store multiple data types in System.Array?

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

Ques:What does the term immutable mean?
Sol: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.

Ques:What’s the difference between System.String and System.Text.StringBuilder classes?
Sol:System.String is immutable. System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

Ques:What’s the advantage of using System.Text.StringBuilder over System.String?
Sol: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.

Ques:What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
Sol:The first one performs a deep copy of the array, the second one is shallow. A shallow copy of an Array copies only the elements of the Array, whether they are reference types or value types, but it does not copy the objects that the references refer to. The references in the new Array point to the same objects that the references in the original Array point to. In contrast, a deep copy of an Array copies the elements and everything directly or indirectly referenced by the elements.

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

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

Ques:What class is underneath the SortedList class?
Sol:A sorted HashTable.

Ques:Will the finally block get executed if an exception has not occurred?

Ques:What’s the C# syntax to catch any possible exception?
Sol: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 {}.

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

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

Ques:Does C# support parameterized properties?
Sol:No. C# does, however, support the concept of an indexer from language spec. An indexer is a member that enables an object to be indexed in the same way as an array. Whereas properties enable field-like access, indexers enable array-like access. As an example, consider the Stack class presented earlier. The designer of this class may want to expose array-like access so that it is possible to inspect or alter the items on the stack without performing unnecessary Push and Pop operations. That is, Stack is implemented as a linked list, but it also provides the convenience of array access.
Indexer declarations are similar to property declarations, with the main differences being that indexers are nameless (the name used in the declaration is this, since this is being indexed) and that indexers include indexing parameters. The indexing parameters are provided between square brackets.

Ques:Can I define a type that is an alias of another type (like typedef in C++)?
Sol:Not exactly. You can create an alias within a single file with the "using" directive: using System; using Integer = System.Int32; // alias
But you can't create a true alias, one that extends beyond the file in which it is declared. Refer to the C# spec for more info on the 'using' statement's scope.

Ques:Is it possible to have different access modifiers on the get/set methods of a property?
Sol:No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property read-only (by only providing a get accessor) and create a private/internal set method that is separate from the property. 

Be creative and Share your skills:
Dear friends, If you have some other technical interview questions mostly asked in other IT companies you can send me at with your complete detail(name, mobile no, email ID). I will post them on code imagine with your details as an author.


sarabjeet said...

Great work, really appreciate your effort for the information and being enrolled in the OOps, .NET and SQL INTERVIEW Preparation i found your information very helpful.

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