Top Research based C# interview Questions with examples

Top Researched Based c# interview Questions with Examples.

What is C#?
C# (pronounced as C-Sharp) is an Object Oriented programming language developed by Microsoft. This language is very similar to Java and was developed to bring together C++ features and the easy programming of Visual Basic (VB).

Difference between C++ and C#?

C#

  • C# is a higher level programming language built over C++ programming language.
  • It is similar to Java.
  • It can be considered as a hybrid programming language consisting of features of C++ and ease of use of VB.Net.

C++

  •  C++ is a low level programming language built by adding object oriented concepts to the C programming language
  • It is NOT similar to Java.
  •  C++ itself is a language and does not inherit any features of other languages.

What is Struct and Class in C#?

Struct

  • Value Type i.e. whenever a variable is created, it holds the value.
  • Copying a Struct variable, copies the value.
  • A new variable is created in Stack memory.
  • Cannot be inherited.
  • Cannot be of Abstract type.
  • Cannot contain Private parameterless constructors.
  • Doesn’t support Destructor.

Class

  • Reference Type i.e. whenever a variable is created, it holds the reference (address) while the value is stored some location.
  •  Copying a Class variable, copies the reference while the value remains on same location.
  •  A new variable is created in Heap memory.
  •  Can be inherited.
  •  Can be of Abstract type.
  • Can contain Private parameterless constructors.
  • Supports Destructor.
  •  Difference between String and StringBuilder in C#?
    String
  •  Belongs to the System namespace.
  • Immutable i.e. whenever you append a String object it creates a new object with new memory allocation.
  • When changed, a new object is created and old object is destroyed.
  • Avoid using inside loops, as if the loop executes N times. N memory allocation operations will be performed.
  • Concat function is used for String concatenation.
Example: string s = “Mudassar”;

s = string.Concat(s, “Khan”);

String Builder

  • Belongs to the System.Text namespace.
  • Mutable i.e. whenever you append a String object it does not creates a new object with new memory allocation.
  • When changed, no new object is created or old object is destroyed.
  • Recommended for loops, as only the size of object will change.
  • Append function is used for String concatenation.
Example: StringBuilder

sb = new StringBuilder();

sb.Append(“Mudassar”);

sb.Append(“Khan”);

What is Static function and example of in-built Static function in .Net

  • Has the keyword static.
  • A Static function is one that can be accessed without creating an object of the class.
  • It can be accessed using the name of the class.
  • It can belong to Static as well as Non-Static classes.
  • One cannot use external Non-Static objects and functions inside a Static method.
  • One can use Static function in Static as well as Non-Static classes.
  •  Keyword this is not supported.

Example of one inbuilt Static function in C# is Convert.ToString().



Example:

public class A { public static void C() { //Invalid this.D(); }

public void D() { //Valid C(); } }

What is Static class and its difference with Non-Static class?

A Static class is a class that cannot be instantiated i.e. its object cannot be created.
Static class

  • Has the keyword static.
  • Cannot be instantiated and no object can be created.
  • Keyword new is not supported.
  •  Objects and Functions can be accessed by class name.
  •  Mandatory for functions and methods to be marked static i.e. can contain only Static members.
  • Members cannot be accessed using this keyword.
  • Only one instance can be created.
Example:

public static class B { public static object E;

public static void F() { }

public static void G() { //Valid var q = E; //Valid F(); } }

Non-Static class

  • Does not have the keyword static.
  •  Can be instantiated and object can be created.
  • Keyword new is supported.
  • Objects and Functions cannot be accessed by class name unless marked static.
  •  Not mandatory for Functions and Methods to be marked Static i.e. can contain Static as well as Non-Static members.
  •  Non-Static members can be accessed using this keyword. But Static members cannot be accessed using this keyword.
  • Multiple instances can be created.
Example:

public class A { public object C;

public static object G;

public static void D() { //Invalid var p = C;

//Valid var q = G;

//Invalid E(); }

public void E() { //Valid. var p = this.C; //Valid var q = G; //Valid D(); } }

What is Namespace in C#? Give example of in-built Namespace in .Net



A Namespace is used to organize classes. Example of in-built .Net Namespace is the System Namespace.

  •  One can create his own Namespace and define the scope of the classes belonging to the Namespace.
  • Keyword using is used in order to access a class belonging to a particular Namespace.
  • A class belonging to a Namespace can be accessed only when the Namespace is made accessible with the help of using directive.
  • A namespace does not have any access modifiers i.e. namespace cannot be public, private, etc.
  • A namespace can belong to multiple assemblies and also a single assembly can have multiple namespaces
Example:

namespace MySpace { public class A { public static void Fun() { } } } namespace YourSpace { //Accesing the Namespace using MySpace; public class B { public void Fun() { //Accessing the class of external namespace A.Fun(); } } }

What is a Sealed class in C#?
A Sealed class is a class which cannot be inherited. The sealed keyword is used to prohibit inheritance of a particular class in C#.
A sealed class can be public as well as private.

Example: public sealed class A { public void Fun() { } } //Compiler Error: ‘B’: cannot derive from sealed type ‘A’ public class B : A { public static void Fun() { } }

public class C { public static void Fun() { //Valid A a = new A();
a.Fun(); } }

What is an Internal class in C#?
An Internal class is a class which cannot be used outside its Assembly. The internal keyword is used to mark a particular class Internal i.e. it restrict its access outside the Assembly.

  • An Assembly could be a Project, a DLL or an EXE.
  • An internal class can be inherited within the Assembly.
Example: internal class A { public void Fun() { } }//Valid public class B : A { public static void Fun() { } } public class C { public static void Fun() {

//Valid A a = new A(); a.Fun();

} }

What is an Abstract class in C#?
An Abstract class is a special class which is majorly used for inheritance and it cannot be instantiated.

  • Cannot be instantiated i.e. object cannot be created using the new keyword.
  • Can contain both Abstract and Non-Abstract members.
  • Abstract members are simply declared and are defined in the classes deriving the Abstract class.
  • Abstract members are defined by using the override keyword.
  • Non-Abstract members are defined within the Abstract class.
  • Non-Abstract members can be accessed within the derived classes only if marked public or protected.
  • Private Non-Abstract members are not accessible outside the Abstract class.
  • Abstract and Non-Abstract members can be accessed using the derived classes.
  •  Does not support Multiple Inheritance.

 

Example: public abstract class A { public abstract void Fun1();

public void Fun4() { } protected void Fun5() { } private void Fun6() { } }

public class B : A { public override void Fun1() { }

public void Fun2() { //Valid Fun4(); Fun5();

//Compiler Error: Cannot create an instance of the abstract class or interface Fun6(); } } public class C { public static void Fun3() {

//Compiler Error: Cannot create an instance of the abstract class or interface ‘A’ A a = new A(); //Valid B b = new B(); b.Fun1(); b.Fun2(); b.Fun4(); } }

What is an Interface in C#?
An Interface is similar to an Abstract class and it also cannot be instantiated.

  • Cannot be instantiated i.e. object cannot be created using the new keyword.
  • Can contain only declaration of Members and not definition.
  • Members are simply declared and are defined in the classes deriving the Interface.
  • Members are defined without using the override keyword.
  •  Cannot contain Access modifiers i.e. Members cannot be public, private, etc.
  • The derived member can only be public.
  •  Does support Multiple Inheritance.
Example: public interface A { void Fun1(); void Fun2(); }

public class B : A { public void Fun1() { }

//Error: ‘B’ does not implement interface member ‘A.Fun2()’

//’B.Fun2()’ cannot implement an interface member because it is not public private void Fun2() { } } public class C { public static void Fun3() {

//Compiler Error: Cannot create an instance of the abstract class or interface ‘A’ A a = new A();

//Valid B b = new B(); b.Fun1(); //Invalid b.Fun2(); } }

 

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