C#

LINQ Average Operator

April 2, 2017 by ashish Leave a Comment

LINQ stands for Language Integrated Query.You can use the Average method to calculate the average of numerical values in a collection.
It returns a single value which is an average of the values in the collection.

If we execute the following then we get the average as 3.

IList<int> list = new List<int>() {1,2,3,4,5};
var avg= list.Average();
Console.WriteLine(avg);

Other than int average can be used with double,float or decimal values also.Following Average function call returns the value 3.2

IList<float> list = new List<float>() {1.5f,2f,3f,4.5f,5f};
var avg= list.Average();
Console.WriteLine(avg);

Calculating average of specific items in a collection using Average function

In the following example we are calculating average of list items after filtering the items.

We have declared student class as:

class Student
{
public string Name { get; set; }
public string Subject { get; set; }
public int Marks { get; set; }
}

We can calculate the marks of a particular student by using the following

IList<Student> list = new List<Student>() {
new Student{Name="Mark",Subject="Maths",Marks=60},
new Student{Name="John",Subject="English",Marks=66},
new Student{Name="Mark",Subject="English",Marks=76},
new Student{Name="Ajay",Subject="Maths",Marks=66}

};
var avg= list.Where(x=>x.Name=="Mark").Select(x=>x.Marks).Average();
Console.WriteLine(avg);

ashish

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C# Interview Questions and Answers for Experienced

March 3, 2017 by ashish Leave a Comment

Following are some of the most important C# Interview Questions and Answers and will help you to understand some of the main concepts of C#.

Some of the basic questions asked in interviews are:

What is an Interface in C# ?

An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body.Interface is implemented by a class.If a class implements an interface then it needs to implement all the members declared in the interface.
Interface can contain methods,properties,indexers and events.
Following interface declares a method called SomeMethod.



interface ISomeInterface

{

void SomeMethod();

}

Someclass implements the ISomeInterface ,so it needs to implement the method declared in the interface.



class Someclass:ISomeInterface

{

public bool void SomeMethod()

{

//implementaion

}

}

Explain what is a constructor in C#?

Constructor is a method of a class which is executed when an instance of a class is created.It is used to perform the class initialization like assigning default values to variables.Though it is just a class method it differs from other methods in these ways
It has the same name as the class name
It does not have any return type
Following is an example of constructor in a class called Employee.Please note that the constructor name is same as the class name,Employee.

class Employee { private string _name; ppublic Employee(string name) { _name=name; } }

What is method overloading in C#?

Method overloading means having different methods in a class with same name but different signatures.Signature of a method includes its parameter types and name.Its important to realize that return type is not part of method signature.

In the following example there are two method overloads of the sum method.The first method accepts two integer arguments while the second overload accepts three integer arguments.
public int Sum(int a,int b) { int sum=a+b; return sum; }

public int Sum(int a,int b,int c) { int sum=a+b+c; return sum; }

Please note that the name of the above two methods is same ,sum.But the two methods differ in the number of arguments making them the overloaded methods.

What is method overriding?

Methods defined in a base class can be overridden in a derived class.This means we can define a method in a derived class with the same signature as the base class.
So we can provide a different implementation of the method defined in the base class.The method which is invoked is determined at runtime depending on the type of object.So if the object reference points to derived class then the derived class method is called and if the reference points to base class then the base class method is called.
class Base { public virtual string Hello() { return "Hello Base"; } }


class Derived : Base

{

public override string Hello()

{

return "Hello Derived";

}

}
class Program

{
static void Main(string[] args)

{

Base objBase = new Derived();

string message = objBase.Hello();

Console.WriteLine(message);
objBase = new Base();

message = objBase.Hello();

Console.WriteLine(message);

Console.ReadLine(); } }
On executing the above code we get the following message

How can we prevent a class from being inherited in C#?

We can prevent class from being inherited by using the Sealed keyword.

sealed class class1
{
     public class1()
      {

      }
}

What are the differences between a struct and a class in C#?

Some of the main differences are

Struct is a value type while class is a reference type
Struct variables are stored on a stack while class objects are stored on a heap
We can not inherit a Struct while we can inherit a class
Struct can not have a default constructor(prior to C# 6) while class can have a default constructor

What are the differences between Interface and Abstract class?

Interface can have only abstract methods while Abstract class can have concrete methods as well.
All interface members are public
A class can implement multiple interfaces while it can derive from only single abstract class

What is managed code?

When we write c# code we are writing managed code since it will be executed by the CLR. Manged code gets several benefits like memory management,security.Unmanaged code is the code which is not executed by the CLR.

What is a static constructor in C# ?

Static constructor is used to initialize static data members of a class.It is called as soon as the class is referenced for the first time, whereas an instance constructor is used to initialize an instance of a class.

What is Polymorphism?

Polymorphism is often referred to as the third pillar of object-oriented programming, after encapsulation and inheritance. Meaning of Polymorphism is many-forms .At run time, objects of a derived class may be treated as objects of a base class.This is an example of runtime polymorphism.

What is abstract class?

An abstract class is the one that is not used to create objects. An abstract class is designed to act as a base class (to be inherited by other classes). Abstract class is a design concept in program development and provides a base upon which other classes

What is Dispose?

Its a method invoked for memory cleanup and releasing unmanaged resources like database connections ,file handles.Class’s that wants to perform cleanup operations implements the Dispose method of the IDispose interface.

What is the difference between Dispose and Finalize?

Finalize
Is called automatically by the garbage collector and can not be called by the user code
It is defined by the Object class
There is performance overhead since it is called by the garbage collector at the time of releasing memory used by the object.
Dispose
It is explicitly called by the user code to cleanup unmanaged resources
It is declared in the IDisposable interface
There is no performance overhead

What are constant and read-only variables in C#?

Constants
constant variables must be assigned a value at the time of declaration and it can not be reassigned after this
We can not use static modifier for a constant field
We can declare constant variables inside methods
Readonly
readonly field be assigned a value at the time of declaration or in the constructor after which it can be reassigned
We can use static modifier with a readonly field
We can not declare readonly variables inside methods

What is the use of “using” statement in C#?

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

How does CLR execute code?

When the c# code is compiled the output of the compilation is MSIL. MSIL stands for Microsoft intermediate language. MSIL instructions are CPU independent i.e they can run on any CPU.It is the job of the CLR to convert the MSIL instructions into executable code that can be executed on the target machine.
What are the different types of assemblies ?
There are two types of assemblies Private and Shared assembly. A private assembly is used by a single application and is stored in application directory.So it is application specific. A shared assembly is stored in the global assembly cache and can be used by different applications.

What is a NameSpace?

NameSpace Logically group types such as classes and interfaces.The types in the framework are grouped into different namespaces e.g the types in System.Data namespace defines the ADO.NET functionality .We bring all the typed defined in a namespace in scope with using statement.

Can we force garbage collector to run?

System.GC.Collect() forces garbage collector to run.
What is reflection?
All .NET assemblies stores metadata information about the different types defined in the assembly. This metadata information can be accessed by using the classes defined in the “Reflection” API.

What are Value types and Reference types?

Value types directly contain their data on the stack.Reference type variables stores a reference to the data’s memory location and are allocated on the heap.Since value type variable contains the value operation on one one value type variable doesn’t impact the other variable.While reference type variable points to the location of the object so operation on one reference type variable effects all the reference which points to the object.

What is Object Oriented Programming?

Object Oriented Programming is a design concept.In object oriented programming the program consists of objects The objects have a certain relationship with each other and communicate with each other .C# is an object oriented programming language since it supports the object oriented concepts.So a c# program consists of objects which defines state and behavior.
Following are the main object oriented concepts:

Polymorphism
Abstraction
Inheritance
Encapsulation

Polymorphism

Polymorphism means have multiple forms.So single interface can represent multiple methods.Examples of polymorphism is method overloading and virtual methods.

Abstraction

Abstraction means refining unimportant details and keeping only the required attributes.

Inheritance

Inheritance means inheriting properties and methods from an existing class. Inheritance helps reuse of existing code since a derived class inherits methods and properties from existing class.

Encapsulation

Encapsulation means hiding internal implementation details of a class and providing access to a class through public interface.Encapsulation in C# is implemented using access modifiers.

What is a extension method in C# ?

Sometimes we need to add new functionality to an existing class without modifying the existing class.We may not have the code of the class available or we don’t want to modify the existing class.In such cases we can use extension methods.

Extension method is a method which is added to an existing class without modifying the existing class.To add a new method to a class:

Declare a static class.
Declare a static method in the static class.
The first parameter of the method should use the this keyword.
The type of the first parameter should be the class type in which you want to add the extension method.

ashish

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Action,Func and Predicate in .NET

August 29, 2016 by ashish Leave a Comment

Delegate in .NET is a type which can refer to a method.So if we have a delegate type declared as

delegate int tempDelegate(int a,int b);

then the above delegate can point to a method which accepts two integer arguments and returns an integer type

tempDelegate objDelegate=Add;
int sum=objDelegate(1,2);

public int Add(int a,int b)
{
return a+b;
}

There are few common signatures of delegates used commonly in the applications.For example many times we need to declare a delegate
which accepts integer arguments and returns integer value.

Instead of declaring delegates for every input and output types .NET framework provides some generic delegates.Action,Func and Predicate in .NET can be used to refer to commonly used methods instead of declaring a new delegate type.

Action<TParameter> delegate points to a method which accepts parameters but does not return any value.
In the following example we have declared an Action<T> delegate which accepts string argument and return void.

Action<string> displayObj = Display;
displayObj("Hello!");

public void DisplayMessage(string message)
{
Console.WriteLine(message);
}

Func<TParameter,TOutput> delegate points to a method which accepts parameters and also returns a value.In the following example we have declared a Func<T> object which accepts two integer arguments and returns an integer.

Func<int, int,int> addObj = Add;
int sum=addObj(2, 4);

Predicate<TParameter> delegate points to a method which accepts parameter and always returns a boolean value.In the following example we have declared Predicate<T> which accepts a Person type object and returns a bool value.

Predicate<Person> personObj = IsPersonAdult;

public bool CheckPersonsAge(Person person)
{
return person.Age < 18;
}

ashish

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Set log4net log file path dynamically in c#

July 7, 2016 by ashish 2 Comments

log4net is an open source library used for logging the information during program execution.It is one of the most popular logging libraries used in c#.

Sometimes we need to decide and set the location of the log file at runtime.To set the log4net log file path dynamically in c# is as simple as defining a property in the config file and setting the property value at
runtime in code

We can use following steps to implement this scenario.

Suppose you have configured log4net in config file as:

<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
<file value="Sample.log" />
<appendToFile value="true" />
<maxSizeRollBackups value="100" />
<rollingStyle value="Size" />

<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date - %message-%newline" />
</layout>
</appender>

<logger name="SampleAppender">
 <level value="DEBUG" />
 <appender-ref ref="RollingFileAppender" />
</logger>

Replace the <file value=”Sample.log” /> element with the below element.The PatternString is a string representing a pattern which could contain different values.One pattern is property which represents a property which is set at runtime.Here we are including a LogFileName property.

<file type="log4net.Util.PatternString" value="%property{LogFileName}.log" />

Please note that we have used %property{LogFileName} to dynamically set the value attribute of the file element.%property{LogFileName} indicates that LogFileName we will set it dynamically.

2. Set the LogFileName value in code.

ILog logger = LogManager.GetLogger("SampleAppender");
log4net.GlobalContext.Properties["LogFileName"] = "MyLog";
XmlConfigurator.Configure();

For the basics of implementing log4net in your application please refer Introduction to log4net in c#

ashish

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Exception handling in C#

June 30, 2016 by ashish Leave a Comment

C# provides managed exception handling.This means that we don’t have to manually check the code for exceptions.Instead execution is automatically transfered to the appropriate part.

An Exception is an error which happens during program execution or runtime.Exception handling allows us to efficiently manage the unexpected behaviors during program execution.For example if we try to assign string value to an integer value during runtime then an exception occurs.

When an exception occurs an object of type derived from the Exception class is created and thrown.Exception is a class in the System namespace. All the exceptions in .NET framework derive from the Exception class.If we need to create our custom exception class then we can derive our class from the Exception class.

Exception handling in C#

C# provides structured exception handling.This means that the exceptions are monitored using the well defined exception handling constructs or keywords. Following are the exception handling keywords

try
catch
finally

try
try keyword defines the try block . try block contains the code which we want to monitor for exceptions.If an exception occurs inside the try block an object of type exception is created and thrown.

catch try block is followed by the catch block.catch keyword defines the catch block.The exception that is thrown by the catch block is handled in the catch block.This mean when exception occurs the control is automatically passed to the catch block.

As there can me multiple catch blocks so the type of exception object determines which catch block will execute.

finally finally block is the last block.This is defined using the finally keyword. Unlike catch and try blocks finally block defined the code which is sure to execute each time.This block usually defined the clean up code such disposing objects.

In the following code there are two catch blocks.The first catch block will handle the exceptions of type Exception1 while the second catch block will handle exceptions of type Exception2

try
{
//code to monitor for exceptions
}
catch(Exception1 exc1)
{
 //exception handling code
}
catch(Exception2 exc2)
{
 //exception handling code
}
finally
{
 //clean up code
}

Causes of exceptions

Exceptions can be automatically thrown by the .NET
Exceptions can be thrown by creating and throwing an object of type exception.

Inbuilt Exception classes

There are few inbuilt exception classes provided by the Framework.These are used for handling different types of exceptions.Some of the commonly used exception classes are:

IndexOutOfRangeException thrown when array refers to an invalid index.
NullReferenceException thrown when a null object is referenced
DivideByZeroException thrown when an attempt is made to divide by zero.
InvalidCastException thrown when the specified cast is invalid.

ashish

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