Krystyna Ślusarczyk Mid Level

Question 1

What is the use of “using” keyword?

Answer 1

Two main uses:

a. The using directive which allows using types from another name spaces, and to create alias.

Example:

using System.Diagnostics;

namespace justFOrLearning
{
    class @using
    {
        Stopwatch sw = Stopwatch.StartNew();
    }
}

We can also make the using as global in C# 10 onwards.

Another example is that if we have conflicts, then we can create the alias.

In file1,.cs

namespace File1
{
   class Person{}
}

In file2,.cs

namespace File1
{
   class Person{}
}

when we do

using file1;
using file2;

Person p = new Person(); //this creats conflicts.

so we can create alias:

using file1Person = file1.person;
using file2Person = file2.person;

Next is using staement ,that defines a scope in which an IDisposable will be used, and disposed at this scpre’s end.

var fileStream = File.Open(“path”, FileMode.Open);

try
{
}

catch
{
filestream.Dispoase;
}

using(var fileStream = File.Open("path", FileMode.Open)
{
   //some operations
}

Question 2

What are global using directives?

Answer 2

Can we used in any file.

Question 3

What is statically-typed and dynamically-types languages?

Answer 3

In statically-typed languages, type checks happen at the compile time.

In Dynamically-typed languages, type checks happen at the runtime time.

Example,JS\

let v = 10;
v= "hey";

No errors here.

this wont happen in C#.

Question 4

What is a dynamic keyword?

Answer 4

A variable declared with Dynamic type will bypass the static type checking.

Question 5

What are weakly typed and strongly typed languages?

Answer 5

res = “2” + 3;

2 will be converted to other type.

In weakly types languages the variable is converted form one type to another. I strongly types languages, this is not the case.

Question 6

What is an expression?

Answer 6

piece code which evalutes to some value.

Question 7

What is a statement?

Answer 7

piece of code but does not evaluate to any value.

Question 8

What is expression-bodied members?

Answer 8

expression-bodied members are members deinfed with expression body instead of the regular body with braces.

class string
{

  public override string ToSTtring(string str)
  {
      //some operations
  }

can be written as

public override string ToSTtring(string str) = //some operations

only one line can be added.

Question 9

what is Func and Actions?

Answer 9

in C#, we can treat functions like any pther types- assign them to variables or pass them as parameters.

Func and Actions allws us to do that.

Ex:

Func func1;

The last parameter of Func is always a return type.

Action is used to represent void functions.

Question 10

What is Lambda expressions?

Answer 10

allows us to define anonymous functions.

(param1, param2) => param1 + param2;

Question 11

What is the difference between throw and throw ex?

Answer 11

Throw preserve the stack trace while throw ex does not preserve the stack trace.

using throw ex, we loose the information about the methods.

Question 12

What is a stack trace?

Answer 12

The stack trace is a trace of all methods that have been called that led to a particular situation in the code.

Question 13

How to log stack trace?

Answer 13

Environemnt.StackTrace.

Question 14

What is the difference between typeof anf GetType?

Answer 14

Both typeof and GetType returns the Type object which holds the information about the type.The inforaon such as properties methods an d constructors.

The GetType is called upon an object so it gets resolved in runtime. It is a aprt of System.Object.

Example:

Class Base
{}

Class Derived : Base
{}

var type = typeof Base;

derivedObj = new Base();
var type = derivedObj.GetType();

GetType always return the actual type.

Question 15

What is checked keyword?

Answer 15

The checked keyword is sued to define a scope in which arithmetic operations will be checked for overflow.

It checks just the scope in which it is defined and not the inner code. I mean if a method is called inside the scope, the code inside the method will not be checked for the overflow.

Checked keyword reduces the performace.

Ex:

checked
{

}

Question 16

What is checked keyword?

Answer 16

The checked keyword is sued to define a scope in which arithmetic operations will be checked for overflow.

It checks just the scope in which it is defined and not the inner code. I mean if a method is called inside the scope, the code inside the method will not be checked for the overflow.

Checked keyword reduces the performance.

Ex:

checked
{

}

Question 17

What is the range of a BYTE?

Answer 17

0 to 255

Question 18

What is unchecked keyword?

Answer 18

Opposite of checked keyword. Used when we set it in the project.

Question 19

What is a silent failure?

Answer 19

The failure happens without the knowledge of a developer.

Example, arithmetic operations overflow.

Question 20

What is BigInt?

Answer 20

Bigint is limited by the application’s memeoty. It represents Gigantic number.

Question 21

What is difference between string and StringBuilder?

Answer 21

Strings are immutable. It means that once we define string it cannot be modified.

For example,

string b = “abc”;
strung add = b + “c”;

STringBuilder strBuilder = New StringBuilder();
strBuilder.Append();

StringBuilder is a utility class used for optimal concatination of strings.

When we append using string,

a. It creates a new string.
b. Points to a new string.
c. GC have to clean old string.

If we want add a string incrementally then we have to use StringBuilder.

Question 22

What is an Array?

Answer 22

Array is a most basic collection in c#.

We can think array as a collection of boxes. Each boxes has an index and hold a vlue.

Arrays are reference types in c#.

Example:
  //Array

        var arr = new int[5];

        arr[0] = 1;

        var arrWithIni = new int[] { 1, 2, 3 };

        var multiDimensionArr = new int [3,3];

        var jaggedArr = new int[2][3];

        jaggedArr[0] = new int[] { 1, 2, 3 };

Question 23

What is a jagged array?

Answer 23

Jagged array is an array of arrays which can be different sizes.

Question 24

What are advantages of arrays?

Answer 24

they are fast and easy to use.

Question 25

What are dis-advantages of arrays?

Answer 25

Arrays are of fixed size.

Question 26

What is a List?

Answer 26

List is a strongly typed generic collections of objects.

To create a List,

//List

        var listOf = new List();

        //List

We can also define Capaciity of the list in the constructor.

When we define the capacity it optimizes by not allocation new size every time we add a new item.

Question 27

Why catch(exception) is a bad idea?

Answer 27

The catch(exception) is bad idea because it catches every type of exception.When we decide to catch an exception we shoud know how to handle the exception.

Question 28

When catch(exception) is OK to use?

Answer 28

in GLobal catch block.

Question 29

What is global catch exception?

Answer 29

the global catch block is the cach block in the upper most layer of the application so that any exception in the application is handled.

Question 30

What are NuGet packages?

Answer 30

NuGet is a Microsoft supported package manager so that developers can create and share their code.

Question 31

What is the difference between Release and debug mode?

Answer 31

In Release mode, there will some optimization so that the program can run faster.

Question 32

If we want to run a piece of code only in debug mode, how to do that?

Answer 32

if DEBUG

Question 33

Does the garbage collector call the Dispose method?

Answer 33

No, GC is not aware of Dispose method. we have to call it. We can use using statement to call.

Question 34

When should be write our own destructors?

Answer 34

Never. Destructors are very tricky and we don’t have a guarantee that they will run. We shoudl use DIpose method instead.

Question 35

What is managed and unmanaged code?

Answer 35

Managed resources are managed by CLR. all objects created in C# are managed resources. GC is aware of their existence and they will clean up when those resources are not needed.

Unmanaged are not managed by C#. GC are not aware of them and GC wont clean them. Unmanaged resources are DB connections and File handlers.We have to perform the clean i

Question 36

What is the difference between Dispose and Finalize?

Answer 36

Dispose method is used to free unmanaged resources. we have to use IDisposable to use Dispose method. Example, File reader class used File handler. We need to close the file handler. We should not put this code in destructor. Instead, we have to use IDisposbale.

The Finalize method is the same thing as the destructor, so it is the method that is called on an object when cleaned up by the garbage collector. We cannot override Finalize method. We get a compiler waring. Instead, we have write a destructor.

Question 37

What is a Tuple?

Answer 37

Tuple is a small data structure used to bind many values together.

For example, if I write a function and I need to return many values, I can use tuples.

To create a tuple,

      var tuple1 = new Tuple(1, "abc");
      var tuple2 = Tuple.Create(1, 5, "this");

Question 38

How many values tuples can hold?

Answer 38

8 because Tuples are reference types.

Question 39

What is a valueTuples?

Answer 39

same as tuple but they are value type. Hence, we can store more then 8 data and == operators returns true.

In tuple we have to use .Equals to compare.

var valTuple = new ValueTuple(2, "abc");
var valTuple2 = (2, "abc");
ValueTuple valTuple3 = (number: 2, text: "hey");

Question 40

Differences between tuple and valueTuple?

Answer 40

Tuples are reference types and ValueTuples are value types.

Tuples are immutable i.e. you cant do tupleVar.item1 = 5;

Tuples can hold only 8 data.

Tuples are less performance then value tuples.

Properties are names item1 , item2…

in ValueTuple, we can name the property while declaring.