C# Interview Questions

By | April 28, 2014

  1. What is the difference between shadow and override
  2. You have an event handler called MyEvent and you want to link the click event of control, MyButton, to use MyEvent, what is the code that will like them together?
  3. Which debugging window allows you to see the methods called in the order they were called?
  4. Which debugging window allows you to see all the name and values of all the variables in scope?
  5. What is wrapper class?is it available in c#?
  6. What is protected internal class in C#
  7. Which keyword is used of specify a class that cannot inherit by other class
  8. Can you create the instance for abstract classes
  9. Can we use Friend Classes or functions in Cthe way we use it in C++
  10. How we can use inheritance and polymorphisms in cprogramming?
  11. How to find exceptions in database
  12. How can objects be late bound in .NET?
  13. Where we can use DLL made in C#.Net
  14. What Datatypes does the RangeValidator Control support?
  15. Constructor is the method which is implicitly created when ever a class is instantiated. Why?
  16. Why multiple Inheritance is not possible in C#?
  17. Why strings are immutable?
  18. This is a Regular expression built for parsing string in vb.net and passed to Regex class. Dim are As Regex = New Regex(”,(?=([^””]*””[^””]*””)*(?![^””]*””))”) What is Cequivalent for this regular expression.
  19. How to convert ocx into DLL
  20. What is the main difference between pointer and delegate with examples?
  21. What is object pooling
  22. How do I read the information from web.config file?
  23. What is the default Function arguments?
  24. What is XML Schema?
  25. How can I check whether a dataset is empty or not in C#.net
  26. Is it possible to inherit a class that has only private constructor?
  27. How do you choose 1 entry point when Cproject has more Main( ) method?
  28. The compiler throws an error if XML comments is not well formed
  29. Which of the following is not a Creserved keyword
  30. By declaring a base class function as virtual we allow the function to be overridden in subclasses
  31. Which of the following can not be declared as virtual
  32. Sealed class can be inherited
  33. Which of the following statements is not true for interfaces
  34. It is not permitted to declare modifier on the members in an interface definition
  35. Interface members can not be declared as
  36. Which method is implicitly called when an object is created
  37. Which of the following statement is invalid with regards to constructor
  38. Constructors can not be static
  39. It is perfectly legitimate to throw exceptions from catch and finally blocks
  40. It is not possible for a delegate to wrap more than 1 methos
  41. In Cevents are actually a special form of delegates
  42. Which preprocessor directive are used to mark that contain block of code is to be treated as a single block
  43. How are the attributes specified in C#
  44. For performing repeated modification on string which class is preferred
  45. In order to use stringbuilder in our class we need to refer
  46. Which of the following is not a member of stringbuilder
  47. Which method is actually called ultimately when Console.WriteLine( ) is invoked
  48. What happens when you create an arraylist as ArrayList Arr=new ArrayList()
  49. What is the output of Vectors.RemoveAt(1)
  50. GetEnumerator( ) of Ienumerable interface returns
  51. How do you add objects to hashtable
  52. If A.equals(B) is true then A.getHashcode & B.getHashCode must always return same hash code
  53. The assembly class is defined in
  54. What is the first step to do anything with assembly
  55. How do you load assembly to running process
  56. Assemblies cannot be loaded side by side
  57. Application Isolation is assured using
  58. Where does the version dependencies recorded
  59. How do you refer parent classes in C#
  60. Which attribute you generally find on top of main method
  61. How do you make a class not instantiable
  62. In a multilevel hierarchy how are the constructors are called
  63. Which utility is used to create resource file
  64. What is the extension of a resource file
  65. A shared assembly must have a strong name to uniquely identify the assembly
  66. Public policy applies to
  67. Stream object can not be initialized
  68. Which of the following has stream as the base class
  69. Which class use to Read/Write data to memory
  70. To Configure .Net for JIT activation what do you do
  71. Which method is used by COM+ to ascertain whether class can be pooled
  72. How do you import Activex component in to .NET
  73. Net Remoting doesn’t allow creating stateless & stateful Remote objects
  74. Windows services created by Capp run only
  75. The Ckeyword int maps to which .NET type
  76. What is an indexer in C#
  77. In the following cases which is not function overloading
  78. How to implement multiple inheritence in C#
  79. In Ca technique used to stream the data is known as
  80. Can static methods be overridable?
  81. What is the use of fixed statement
  82. What is the order of destructors called in a polymorphism hierarchy
  83. How can you sort the elements of the array in descending order
  84. Is it possible to Override Private Virtual methods
  85. What does the volatile modifier do
  86. What is the Cequivalent of System.Single
  87. A single line comments are implemented by
  88. Code running under the control of CLR is often referred as
  89. Platform specific code is obtained when
  90. Intermediate Language also facilitates language interoperability
  91. Which are the important features of IL
  92. NET interfaces are not derived from IUnknown & they do not have associated GUID’s
  93. Code written in C cannot used in which of the languages
  94. It is not possible to debug the classes written in other .Net languages in a Cproject.
  95. Which of the following is not a subclass of Value Type class
  96. Which of the following is not a subclass of reference type
  97. Which is .NET s answer to Memory Management
  98. .NET run time relies on the object reference counts to manage memory
  99. What are Namespaces
  100. Which of the following keyword is used along with Main function in C#

=================================================================================================  

  • what is the main difference between delegate and an event in c#?
  • How to use HASH TABLE,ARRAYLIST in c# explain with example?
  • Assemblies are of the following types:
  • What is the difference between shadow and override
  • What is the top .NET class that everything is derived from?
  • C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write?
  • When you inherit a protected class-level variable, who is it available to?
  • Does C# support multiple inheritance?
  • How do you inherit from a class in C#?
  • What is an abstract class?
  • What does the keyword virtual mean in the method definition?
  • How’s method overriding different from overloading?
  • What’s the top .NET class that everything is derived from?
  • Describe the accessibility modifier protected internal.
  • Are private class-level variables inherited?
  • When you inherit a protected class-level variable, who is it available to?
  • Does C# support multiple inheritance?
  • How do you inherit from a class in C#?
  • What’s the implicit name of the parameter that gets passed into the class’ set method?
  • Is it mandatory to implement all the methods which are there in abstract class if we inherit that abstract class..?

=============================================================================================================

  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 {}.
  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.

========================================================================================================= 1.Does C# support multiple-inheritance? No. But you can use Interfaces.2.Where is a protected class-level variable available? It is available to any sub-class derived from base class 3.Are private class-level variables inherited? Yes, but they are not accessible. 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. 6.Which class is at the top of .NET class hierarchy? System.Object. 7.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. 8.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. 9.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. 10.Can you store multiple data types in System.Array? No. 11.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. 12.How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods. 13.What’s the .NET collection class that allows an element to be accessed using a unique key? HashTable. 14.What class is underneath the SortedList class? A sorted HashTable. 15.Will the finally block get executed if an exception has not occurred? Yes. 16.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 {}. 17.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 . 18.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). =============================================================================================================

  1. 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.
  2. Can you store multiple data types in System.Array? No.
  3. 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.
  4. How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods.
  5. What’s the .NET datatype that allows the retrieval of data by a unique key? HashTable.
  6. What’s class SortedList underneath? A sorted HashTable.
  7. Will finally block get executed if the exception had not occurred? Yes.
  8. 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 {}.
  9. 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.
  10. 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.
  11. What’s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
  12. What’s a multicast delegate? It’s a delegate that points to and eventually fires off several methods.
  13. 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.
  14. What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command.
  15. 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.
  16. What namespaces are necessary to create a localized application? System.Globalization, System.Resources.
  17. What’s the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments.
  18. How do you generate documentation from the C# file commented properly with a command-line compiler? Compile it with a /doc switch.
  19. What’s the difference between <c> and <code> XML documentation tag? Single line code example and multiple-line code example.
  20. Is XML case-sensitive? Yes, so <Student> and <student> are different elements.
  21. 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.
  22. 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.
  23. 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.
  24. 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.
  25. 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.
  26. Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.
  27. How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger.
  28. 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).
  29. 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.
  30. Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
  31. 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.
  32. 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.
  33. 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%’.
  34. 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).
  35. What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
  36. Which one is trusted and which one is untrusted? Windows Authentication is trusted because the username and password are c

Leave a Reply