C#

Question 1

What is Jagged Array in C#?

Answer 1

A Jagged array is an array of arrays.

Question 2

Which class acts as a base class for all the data types in .Net?

Answer 2

System.Object

Question 3

What is boxing/unboxing in C#?

Answer 3

When a value type is converted to object type and when an object type is converted back to a value type.

Question 4

What are the ways that parameters can be passed to a method?

Answer 4

Value, Reference (and Output).

Value parameters hold a copy of the passed value.

Reference parameters holds a reference to the memory location of an argument.

Output parameters are uninitialized reference variables. They allow the method to return more than one value.

Question 5

Can multiple values be returned from a function in C#?

Answer 5

Normally a function can only return a single value but by using output parameters, you can return more than one value from a function.

Question 6

What are dynamic type variables in C#?

Answer 6

Dynamic data type can store any type of value. Type checking for these takes place at run-time.

Example:

dynamic d = 20;

Question 7

What are Value and Reference types and whats the difference between them?

Answer 7

A Value type holds the data within its own memory allocation and a Reference type contains an address to another memory location that holds the real data.

Reference Type variables are stored in the heap while Value Type variables are stored in the stack.

Question 8

What is the difference between the dynamic type and the object type variables?

Answer 8

Dynamic types are similar to Object types except that type checking for Object types takes place at compile time, whereas the Dynamic type is type checked at run time.

Question 9

Whats the difference between String and StringBuilder?

Answer 9

Strings are immutable (their values cannot be changed once they have been created) so any modification to a string value results in a completely new string instance. The mutable System.Text.StringBuilder class should be used when string values will change.

Question 10

Can multiple catch blocks be executed?

Answer 10

No, the first matching catch block will be executed.

Question 11

What is the using statement for?

Answer 11

The using block is used to obtain a resource and then automatically dispose of that resource when the execution of block is completed.

Question 12

What is serialization?

Answer 12

Serialization is the process of converting an object into its binary format.

Question 13

Can “this” be used within a static method?

Answer 13

No because “this” refers to the current instance and static methods are just call and used, there are no instances created.

Question 14

What are indexers in C# .NET?

Answer 14

Indexers allows the instances of a class to be indexed in the same way as array.

Question 15

What is difference between the “throw” and “throw ex” in .NET?

Answer 15

The “throw” statement will show the entire error stack whereas “throw ex” will only show the stack trace from the point where the exception is thrown.

Question 16

What are C# attributes?

Answer 16

An attribute is a declarative tag placed above classes, methods, etc. that is used to convey behavioral
information to the runtime.

Question 17

What is difference between the “is” and “as” operators in C#?

Answer 17

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

Question 18

What are extension methods?

Answer 18

Extension methods allow you to add methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.

Question 19

What is an interface?

Answer 19

An Interface is a class with no implementation. The only thing that it contains is the declaration of methods, properties, and events.

An interface only has public methods declarations without definitions. These abstract methods must be implemented in the inherited classes.

Question 20

What’s the difference between an interface and abstract class?

Answer 20

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.

Question 21

What are the SOLID principles?

Answer 21

SOLID is a mnemonic acronym for five design principles intended to make software designs more understandable, flexible and maintainable.

1. Single responsibility principle
   (All classes and methods should have only a single responsibility.)
2. Open Closed principle
   (Software entities should be open for extension, but closed for modification.)
3. Liskov Substitution principle
   (Objects in a program should be replaceable with instances of their subtypes.)
4. Interface Segregation principle
   (Many specific interfaces are better than one general-purpose interface.)
5. Dependency Inversion principle
   (Depend upon abstractions, not concretions and create loosely coupled code.)

Question 22

What are the fundamental concepts of Object Oriented Programming?

Answer 22

Abstraction – It is a process of identifying the critical behavior and data of an object and eliminating the irrelevant details.

Encapsulation – The Internal representation of an object is hidden from the view outside object’s definition.

Inheritance – It is the ability to create new classes from another class.

Polymorphism – The name means, one name, many forms. It is achieved by having multiple methods with the same name but different implementations.

Question 23

What is Managed code?

Answer 23

This refers to any code that runs on the .Net framework Common Language Runtime.

Question 24

What is a Sealed class?

Answer 24

Sealed classes cannot be inherited.

Question 25

What is a Partial class?

Answer 25

Partial classes are classes that are divided up between multiple .cs files.

Question 26

What is an Abstract class?

Answer 26

Abstract classes cannot be instantiated, only inherited. They should contain at least one method.

Question 27

What is a Static class?

Answer 27

Static classes are not instantiated but called and used directly.

Question 28

What are the differences between a Class and a Struct?

Answer 28

Classes supports inheritance but Structs do not. Classes are passed by reference whereas Structs are passed by value.

Question 29

What is the difference between Virtual methods and Abstract methods?

Answer 29

Virtual methods have a default implementation that can optionally be overridden (using the Override keyword) in the derived class.
Abstract methods however do not have any implementation and the derived classes are required to implement the abstract methods.

Question 30

What are namespaces in .Net?

Answer 30

Namespaces refers to the organize of .Net class and other items into logically groups.

Question 31

What is Abstraction?

Answer 31

Abstraction refers to displaying only the essential features of the class and hiding the unnecessary information.

Question 32

What is the difference between the Continue and Break Statement?

Answer 32

The Break statement completely exits out of the loop. The Continue statement however only exits out of the current iteration of the loop.

Question 33

What are Regular expressions?

Answer 33

Regular expression is a template to match a set of input.

Question 34

What is Parsing?

Answer 34

Parsing is converting a string into another data type.

Question 35

What is a Delegate?

Answer 35

A Delegate is a variable that holds the reference to a method. Hence it is a function pointer of reference type. The delegate and the method that it refers to can have the same signature.

Question 36

What are the different types of Delegates?

Answer 36

Single, multicast and generic.

A single delegate can call a single method.

A multicast delegate can call multiple methods.

Generic Delegate – It does not require an instance of delegate to be defined. It is of three types, Action, Funcs and Predicate.

Question 37

What is Reflection in C#?

Answer 37

Reflection is the ability to access the metadata of the assembly during runtime.

Question 38

What are Generics?

Answer 38

Generics allows you to create classes and methods that do not have any specific data type. The data type is assigned during run-time.

Question 39

What is a process?

Answer 39

A “process” is a program that has been loaded into memory along with all the resources it needs to operate.

Question 40

What are deadlocks?

Answer 40

A Deadlock is where two or more processes are waiting for each other to finish so neither can complete. This usually occurs in multi-threading.

Question 41

What is a Thread pool?

Answer 41

A Thread pool is a collection of threads. These threads can be used to perform tasks without disturbing the primary thread. Once the thread completes the task, the thread returns to the pool.

Question 42

What are pointer types in C#?

Answer 42

Pointer type variables store the memory address of another type.
Example:
char* cptr;
int* iptr;

Question 43

What’s the difference between Polymorphism vs Inheritance?

Answer 43

Inheritance refers to using the structure and behavior of a parent class in a derived class.

Polymorphism refers to changing the behavior of a parent class in the derived class.

Examples of Polymorphism would be:
At run-time
When virtual methods of a parent class are overridden in derived class.
Or
When instances of a derived class are used in place of a their parent class.

Question 44

What are the types of classes in C#?

Answer 44

Static class - These cannot be inherited from or instantiated.

Partial class - These allow its members to partially divide or share source (.cs) files.

Abstract class - These are used as base classes to inherit from and cannot be instantiated.

Sealed class - These cannot be inherited but can be instantiated.

Question 45

What is an abstract class?

Answer 45

An abstract class serves only as a base class for other classes to inherit from, it cannot be instantiated. It’s used to define base types with a common set of behaviors or properties that derived classes should have.

Question 46

What is the difference between an abstract class and an interface?

Answer 46

An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it.