C Sharp Interview Questions and Answers

Answer: C# is an elegant and type-safe object-oriented language that enables developers to build a variety of secure and robust applications that run on the .NET Framework. You can use C# to create traditional Windows client applications, XML Web services, distributed components, client-server applications, database applications, and much, much more. Visual C# provides an advanced code editor, convenient user interface designers, integrated debugger, and many other tools to make it easier to develop applications based on version 4.0 of the C# language and version 4.0 of the .NET Framework.   C# syntax is highly expressive, yet it is also simple ...

Answer: Namespaces are used to organize classes within the .NET Framework. They dictate the logical structure of the code. They are analogous to Java packages, with the key difference being Java packages define the physical layout of source files (directory structure) while .NET namespaces do not. However, many developers follow this approach and organize their C# source files in directories that correlate with namespaces. The .NET Framework has namespaces defined for its many classes, such as System.Xml--these are utilized via the using statement. Namespaces are assigned to classes via the namespace keyword.

Answer: A constructor is a class member executed when an instance of the class is created. The constructor has the same name as the class, and it can be overloaded via different signatures. Constructors are used for initialization chores.

Answer: The GAC is the Global Assembly Cache. Shared assemblies reside in the GAC; this allows applications to share assemblies instead of having the assembly distributed with each application. Versioning allows multiple assembly versions to exist in the GAC--applications can specify version numbers in the config file. The gacutil command line tool is used to manage the GAC.

Answer: Immutable means string values cannot be changed once they have been created. Any modification to a string value results in a completely new string instance, thus an inefficient use of memory and extraneous garbage collection. The mutable System.Text.StringBuilder class should be used when string values will change.

Answer: DLL Hell describes the difficulty in managing DLLs on a system; this includes multiple copies of a DLL, different versions, and so forth. When a DLL (or assembly) is loaded in .NET, it is loaded by name, version, and certificate. The assembly contains all of this information via its metadata. The GAC provides the solution, as you can have multiple versions of a DLL side-by-side.

Answer: Methods are overloaded via different signatures (number of parameters and types). Thus, you can overload a method by having different data types, different number of parameters, or a different order of parameters.

Answer: The sealed keyword prohibits a class from being inherited.

Answer: The Main method.

Answer: You put an @ sign in front of the double-quoted string. String ex = @"This has a carriage returnrn"

Answer: C sharp is a programing language

Answer: Object-oriented programming (OOP) is a programming language model organized around objects rather than "actions" and data rather than logic. Historically, a program has been viewed as a logical procedure that takes input data, processes it, and produces output data.

Answer: C# is a OOPs language, .net framework use to compiled it, to generate machine code.

Answer: Single line comments// for single line commentsMultiple line comments/* for multi line comments */XML tags comments/// XML tags displayed in a code comment

Answer: Boolean ConditionsAutomatic Garbage CollectionStandard LibraryAssembly VersioningProperties and EventsDelegates and Events ManagementEasy-to-use GenericsIndexersConditional CompilationSimple MultithreadingLINQ and Lambda ExpressionsIntegration with Windows

Answer: a set or category of things having some property or attribute in common and differentiated from others by kind, type, or quality.

Answer: Objects are created from Classes, in C#, is an instance of a class that is created dynamically. Object is also a keyword that is an alias for the predefined type System.

Answer: A is special method of the class that will be automatically invoked when an instance of the class is created is called as constructor.Constructors are mainly used to initialize private fields of the class while creating an instance for the class.When you are not creating a constructor in the class, then compiler will automatically create a default constructor in the class that initializes all numeric fields in the class to zero and all string and object fields to null.Syntax.[Access Modifier] ClassName([Parameters]){}

Answer: first element is 0 (zero). In a Array.

Answer: In Overriding methods it will create two or more methods with same name and same parameter in different classes.while Overloading it will create more then one method with same name but different parameter in same class.

Answer: The abstract keyword enables you to create classes and class members that are incomplete and must be implemented in a derived class.The sealed keyword enables you to prevent the inheritance of a class or certain class members that were previously marked virtual.

Answer: A static class is basically the same as a non-static class, but there is one difference: a static class cannot be instantiated.In other words, you cannot use the new keyword to create a variable of the class type. Because there is no instance variable, you access the members of a static class by using the class name itself.

Answer: A non-static class can contain static methods, fields, properties, or events.The static member is callable on a class even when no instance of the class has been created. The static member is always accessed by the class name, not the instance name. Only one copy of a static member exists, regardless of how many instances of the class are created.Static methods and properties cannot access non-static fields and events in their containing type, and they cannot access an instance variable of any object unless it is explicitly passed in a method parameter.

Answer: All types and type members have an accessibility level, which controls whether they can be used from other code in your assembly or other assemblies.You can use the following access modifiers to specify the accessibility of a type or member when you declare it:public: The type or member can be accessed by any other code in the same assembly or another assembly that references it.private: The type or member can be accessed only by code in the same class or struct.protected: The type or member can be accessed only by code in the same class or struct, or in a class that is derived from that class.internal: The type or member ...

Answer: bool, byte, char, decimal, double, float, int, long, sbyte, short, uint, ulong, ushort.More question coming soon.. we are updating our list of ques and answer... :)keep wait and watch for few days.

Answer: We create sealed classes when we want to restrict the class to be inherited. Sealed modifier used to prevent derivation from a class. If we forcefully specify a sealed class as base class then a compile-time error occurs.

Answer: Delegates are same are function pointers in C++ but the only difference is that they are type safe unlike function pointers. Delegates are required because they can be used to write much more generic type safe functions.

Answer: Structs are value-type variables and classes are reference types. Structs stored on the stack, causes additional overhead but faster retrieval. Structs cannot be inherited.

Answer: “is” operator is used to check the compatibility of an object with a given type and it returns the result as Boolean. “as” operator is used for casting of object to a type or a class

Answer: C# provides developers a way to define declarative tags on certain entities eg. Class, method etc. are called attributes. The attribute’s information can be retrieved at runtime using Reflection.

Answer: You are trying to use something that is null (or Nothing in VB.NET). This means you either set it to null, or you never set it to anything at all. Like anything else, null gets passed around. If it is null in method "A", it could be that method "B" passed a null to method "A". The rest of this article goes into more detail and shows mistakes that many programmers often make which can lead to a NullReferenceException.

Answer: private delegate void SetControlPropertyThreadSafeDelegate(    Control control,     string propertyName,     object propertyValue);public static void SetControlPropertyThreadSafe(    Control control,     string propertyName,     object propertyValue){  if (control.InvokeRequired)  {    control.Invoke(new SetControlPropertyThreadSafeDelegate                   (SetControlPropertyThreadSafe),     new object[] { control, propertyName, ...

Answer: You need to use reflection to get the method to start with, then "construct" it by supplying type arguments with MakeGenericMethod: MethodInfo method =typeof(Sample).GetMethod("GenericMethod");MethodInfo generic = method.MakeGenericMethod(myType); generic.Invoke(this,null); EDIT: For a static method, pass null as the first argument to Invoke. That's nothing to do with generic methods - it's just normal reflection.

Answer: Excel does not quit because your app is still holding references to COM objects. I guess you're invoking at least one member of a COM object without assigning it to a variable. For me it was the excelApp.Worksheets object which I directly used without assigning it to a variable: Worksheet sheet = excelApp.Worksheets.Open(...);...Marshal.ReleaseComObject(sheet); What I didn't know was that internally C# created a wrapper for the Worksheets COM object which didn't get released by my code (because I wasn't aware of it) and was the cause why Excel was not unloaded. I found the solution to my problem on this page, which also has a nice rule for th...

Answer: Structs are value types which means they are copied when they are passed around. So if you change a copy you are changing only that copy, not the original and not any other copies which might be around. If your struct is immutable then all automatic copies resulting from being passed by value will be the same. If you want to change it you have to consciously do it by creating a new instance of the struct with the modified data. (not a copy)

Answer: public static string ByteArrayToString(byte[] ba){  StringBuilder hex = new StringBuilder(ba.Length * 2);  foreach (byte b in ba)    hex.AppendFormat("{0:x2}", b);  return hex.ToString();}

Answer: const int SECOND = 1;const int MINUTE = 60 * SECOND;const int HOUR = 60 * MINUTE;const int DAY = 24 * HOUR;const int MONTH = 30 * DAY;var ts = new TimeSpan(DateTime.UtcNow.Ticks - yourDate.Ticks);double delta = Math.Abs(ts.TotalSeconds);if (delta < 0){  return "not yet";}if (delta < 1 * MINUTE){  return ts.Seconds == 1 ? "one second ago" : ts.Seconds + " seconds ago";}if (delta < 2 * MINUTE){  return "a minute ago";}if (delta < 45 * MINUTE){  return ts.Minutes + " minutes ago";}if (delta < 90 * MINUTE){  return "an hour ago";}if (delta < 24 * HOUR){  return ts.Hours + " hours ago";}if (delta &lt...

Answer: Properties expose fields. Fields should (almost always) be kept private to a class and accessed via get and set properties. Properties provide a level of abstraction allowing you to change the fields while not affecting the external way they are accessed by the things that use your class. publicclassMyClass{// this is a field. It is private to your class and stores the actual data.privatestring _myField;// this is a property. When you access it uses the underlying field, but only exposes// the contract that will not be affected by the underlying fieldpublicstringMyField{ get {return _myField;}set{ _myField = value;}}}

Answer: Yes, it is important if your item will be used as a key in a dictionary, or HashSet<T>, etc - since this is used (in the absence of a custom IEqualityComparer<T>) to group items into buckets. If the hash-code for two items does not match, they may never be considered equal (Equals will simply never be called). The GetHashCode() method should reflect the Equals logic; the rules are: if two things are equal (Equals(...) == true) then they must return the same value for GetHashCode() if the GetHashCode() is equal, it is not necessary for them to be the same; this is a collision, and Equals will be called to see if it is a real equali...

Answer: You'll want to modify the manifest that gets embedded in the program. This works on VS2008 and higher: Project + Add New Item, select "Application Manifest File". Change the <requestedExecutionLevel> element to: <requestedExecutionLevel level="requireAdministrator" uiAccess="false"/> The user gets the UAC prompt when they start the program. Use wisely, their patience can wear out quickly.

Answer: Modern, general-purpose programming language Object oriented. Component oriented. Easy to learn. Structured language. It produces efficient programs. It can be compiled on a variety of computer platforms. Part of .Net Framework.

Answer: Basically constructors are 5 types those are Default Constructor Parameterized Constructor Copy Constructor Static Constructor Private Constructor

Answer: C# is an object oriented, type safe and managed language that is compiled by .Net framework to generate Microsoft Intermediate Language.

Answer: No, Multiple catch blocks can’t be executed. Once the proper catch code executed, the control is transferred to the finally block and then the code that follows the finally block gets executed.

Answer: Public declared variables or methods are accessible anywhere in the application. Static declared variables or methods are globally accessible without creating an instance of the class. The compiler stores the address of the method as the entry point and uses this information to begin execution before any objects are created. And Void is a type modifier that states that the method or variable does not return any value

Answer: A constructor is a member function in a class that has the same name as its class. The constructor is automatically invoked whenever an object class is created. It constructs the values of data members while initializing the class.

Answer: The array which has elements of type array is called jagged array. The elements can be of different dimensions and sizes. We can also call jagged array as Array of arrays.

Answer: An argument passed as ref must be initialized before passing to the method whereas out parameter needs not to be initialized before passing to a method.

Answer: The using block is used to obtain a resource and use it and then automatically dispose of when the execution of block completed.

Answer: We can’t use ‘This’ in a static method because we can only use static variables/methods in a static method.

Answer: Constant variables are declared and initialized at compile time. The value can’t be changed after wards. Read-only variables will be initialized only from the Static constructor of the class. Read only is used only when we want to assign the value at run time.

Answer: Interface is an abstract class which has only public abstract methods and the methods only have the declaration and not the definition. These abstract methods must be implemented in the inherited classes.

Answer: Custom Controls are controls generated as compiled code (Dlls), those are easier to use and can be added to toolbox. Developers can drag and drop controls to their web forms. Attributes can be set at design time. We can easily add custom controls to Multiple Applications (If Shared Dlls), If they are private then we can copy to dll to bin directory of web application and then add reference and can use them. User Controls are very much similar to ASP include files, and are easy to create. User controls can’t be placed in the toolbox and dragged – dropped from it. They have their design and code behind. The file extension for user c...

Answer: In an array, we can have items of the same type only. The size of the array is fixed. An arraylist is similar to an array but it doesn’t have a fixed size.

Answer: System.String is immutable. When we modify the value of a string variable then a new memory is allocated to the new value and the previous memory allocation released. System.StringBuilder was designed to have concept of a mutable string where a variety of operations can be performed without allocation separate memory location for the modified string.

Answer: Using Clone() method, we creates a new array object containing all the elements in the original array and using CopyTo() method, all the elements of existing array copies into another existing array. Both the methods perform a shallow copy.

Answer: Using Sort() methods followed by Reverse() method.

Answer: Interfaces have all the methods having only declaration but no definition. In an abstract class, we can have some concrete methods. In an interface class, all the methods are public. An abstract class may have private methods.  

Answer: Dispose() is called when we want for an object to release any unmanaged resources with them. On the other hand Finalize() is used for the same purpose but it doesn’t assure the garbage collection of an object.

Answer: Circular reference is situation in which two or more resources are interdependent on each other causes the lock condition and make the resources unusable.

Answer: Generics are used to make reusable code classes to decrease the code redundancy, increase type safety and performance. Using generics, we can create collection classes. To create generic collection, System.Collections.Generic namespace should be used instead of classes such as ArrayList in the System.Collections namespace. Generics promotes the usage of parameterized types.

Answer: An object pool is a container having objects ready to be used. It tracks the object that is currently in use, total number of objects in the pool. This reduces the overhead of creating and re-creating objects.

Answer: ArgumentException, ArgumentNullException , ArgumentOutOfRangeException, ArithmeticException, DivideByZeroException ,OverflowException , IndexOutOfRangeException ,InvalidCastException ,InvalidOperationException , IOEndOfStreamException , NullReferenceException , OutOfMemoryException , StackOverflowException etc.  

Answer: Sometimes there are some errors that need to be handeled as per user requirements. Custom exceptions are used for them and are used defined exceptions.

Answer: Colon is used as inheritance operator in C#. Just place a colon and then the class name. publicclassDerivedClass:BaseClass

Answer: In method overriding, we change the method definition in the derived class that changes the method behavior. Method overloading is creating a method with the same name within the same class having different signatures.

Answer: Methods can be overloaded using different data types for parameter, different order of parameters, and different number of parameters.

Answer: In an interface, we have virtual methods that do not have method definition. All the methods are there to be overridden in the derived class. That’s why they all are public.

Answer: Declare the class as public and make the method sealed to prevent it from being overridden.

Answer: Implement is up to you as the method is inside your own class. There might be problem when the methods from different interfaces expect different data, but as far as compiler cares you’re okay.

Answer: In singleton pattern, a class can only have one instance and provides access point to it globally. Eg:{ private static readonly singleton _instance=new singleton(); }

Answer: DirectCast is used to convert the type of an object that requires the run-time type to be the same as the specified type in DirectCast. Ctype is used for conversion where the conversion is defined between the expression and the type.

Answer: C# is managed code because Common language runtime can compile C# code to Intermediate language.

Answer: using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;public class Person{ DateTime dob; public DateTime Dob { get{return dob;} set{dob=value;} }public void DisplayDetails(){ Console.WriteLine(calculateAge(dob));}public static int calculateAge(DateTime dob){ int age=0; age=DateTime.Now.Year-dob.Year; return age; }}namespace DateEx1 //DO NOT CHANGE the namespace name{ public class Program //DO NOT CHANGE the class name { public static void Main(string[] args) //DO NOT CHANGE the 'Main' method signature { Person person=new Person(); Console.WriteLine("Enter the date of birth (dd-mm-yyyy):...

Answer: C# is widely-used to create games using the Unity game engine, which is the most popular game engine today. More than a third of top games are made with Unity, and there are approximately 770 million active users of games created using the Unity engine. Unity is also used for VR, with 90% of all Samsung Gear and 53% of all Oculus Rift VR games developed using Unity.