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C# Beyond Basics

bookWhat are Lists?

Imagine we have a situation where we want to store the names of all the students that are taking a certain course. The first solution we can come up is to create an Array:

index.cs

index.cs

copy

              
123456

            
using System;

class Program
{
    string[] studentNames = new string[50];
}

However, if at some point are more than 50 students, we won't be able to store their names. Similarly, in a situation where there are less than 50 students, the unoccupied spaces in the array will be a waste of memory - this becomes a problem in especially large arrays.

Here we need a new structure which can store a variable amount of elements. Luckily such a structure already exists, it's called a List.

Lists are very similar to Arrays, however the number of elements that are stored in a list are changeable.

Following is the syntax for declaring an empty list:

Using this syntax we can create a list for storing the Students' names:

index.cs

index.cs

copy

              
12345678910

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
    	List<string> students = new List<string>();
  	}
}

It is important to note that we need to import the Generic module to be able to use Lists.

You simply need to add this line under using System; to import the required module.

Add() Method

We can add elements to a list by using the Add method:

index.cs

index.cs

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123456789101112131415

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        students.Add("Anna");
        students.Add("Laura");
        students.Add("Jacob");
        students.Add("Aron");
    }
}

The above code will add four elements to the students list.

Just like an Array of type string can only contain string elements. A list of type string can only accept string elements.

Indexing

The first element is Anna hence it will have the index 0, while Laura will have the index 1 and so on. Elements of a list can be accessed via indexing just like an array:

index.cs

index.cs

copy

              
1234567891011121314151617

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        students.Add("Anna");
        students.Add("Laura");
        students.Add("Jacob");
        students.Add("Aron");

        Console.WriteLine(students[2]);
    }
}

Count() Method

We can retrieve the length of a list using its Count attribute:

index.cs

index.cs

copy

              
123456789101112131415161718

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        students.Add("Anna");
        students.Add("Laura");
        students.Add("Jacob");
        students.Add("Aron");

        Console.WriteLine(students[2]);
        Console.WriteLine(students.Count);
    }
}

Dynamic Length

Note that the length of a list is dynamic (changeable), so it changes as we add elements:

index.cs

index.cs

copy

              
1234567891011121314151617181920

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        Console.WriteLine(students.Count);
        students.Add("Anna");
        Console.WriteLine(students.Count);
        students.Add("Laura");
        Console.WriteLine(students.Count);
        students.Add("Jacob");
        Console.WriteLine(students.Count);
        students.Add("Aron");
        Console.WriteLine(students.Count);
    }
}

Initialization

We can also initialize a list with some elements using the following syntax:

List<dataType> listName = new List<dataType>{ element1, element2, … };

For-example:

index.cs

index.cs

copy

              
12345678910111213141516

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string> { "Anna", "Laura", "Jacob", "Aron" };

        // It is still possible to add additional elements after initialization
        students.Add("Markus"); 

        Console.WriteLine(students.Count);
        Console.WriteLine(students[4]);
    }
}

Looping Through Lists

Looping through a List similar to how we would loop through Arrays

- Using a for-loop:

index.cs

index.cs

copy

              
123456789101112131415

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string> { "Anna", "Laura", "Jacob", "Aron" };

        for (int i = 0; i < students.Count; i++)
        {
            Console.WriteLine(students[i]);
        }
    }
}

- Using a foreach loop

index.cs

index.cs

copy

              
123456789101112131415

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string> { "Anna", "Laura", "Jacob", "Aron" };

        foreach (string studentName in students)
        {
            Console.WriteLine(studentName);
        }
    }
}

Tip:

To make the declaration syntax shorter we can also use implicit declaration. To recall, an explicit declaration is when we specify the data type during variable declaration, for-example:

index.cs

index.cs

copy

              
1

            
float number = 7.9f;

On the other hand, in implicit declaration we can simply use the var keyword and the compiler automatically infers the data type of the variable according to the assigned value:

index.cs

index.cs

copy

              
1

            
var number = 7.9f;

We can use implicit declaration when declaring lists as well:

var listName = new List<dataType>();
// or
var listName = new List<dataType>{ element1, element2, … };

For-example:

index.cs

index.cs

copy

              
1

            
var numbers = new List<int> { 1, 2, 3, 4, 5 };

1. What will be the output of the following code:

2. Which module is needed to be imported for using lists?

3. Which method is used for retrieving the size (length) of a list?

question mark

What will be the output of the following code:

Select the correct answer

question mark

Which module is needed to be imported for using lists?

Select the correct answer

question mark

Which method is used for retrieving the size (length) of a list?

Select the correct answer

Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 1. Kapitel 1

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bookWhat are Lists?

Stryg for at vise menuen

Imagine we have a situation where we want to store the names of all the students that are taking a certain course. The first solution we can come up is to create an Array:

index.cs

index.cs

copy

              
123456

            
using System;

class Program
{
    string[] studentNames = new string[50];
}

However, if at some point are more than 50 students, we won't be able to store their names. Similarly, in a situation where there are less than 50 students, the unoccupied spaces in the array will be a waste of memory - this becomes a problem in especially large arrays.

Here we need a new structure which can store a variable amount of elements. Luckily such a structure already exists, it's called a List.

Lists are very similar to Arrays, however the number of elements that are stored in a list are changeable.

Following is the syntax for declaring an empty list:

Using this syntax we can create a list for storing the Students' names:

index.cs

index.cs

copy

              
12345678910

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
    	List<string> students = new List<string>();
  	}
}

It is important to note that we need to import the Generic module to be able to use Lists.

You simply need to add this line under using System; to import the required module.

Add() Method

We can add elements to a list by using the Add method:

index.cs

index.cs

copy

              
123456789101112131415

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        students.Add("Anna");
        students.Add("Laura");
        students.Add("Jacob");
        students.Add("Aron");
    }
}

The above code will add four elements to the students list.

Just like an Array of type string can only contain string elements. A list of type string can only accept string elements.

Indexing

The first element is Anna hence it will have the index 0, while Laura will have the index 1 and so on. Elements of a list can be accessed via indexing just like an array:

index.cs

index.cs

copy

              
1234567891011121314151617

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        students.Add("Anna");
        students.Add("Laura");
        students.Add("Jacob");
        students.Add("Aron");

        Console.WriteLine(students[2]);
    }
}

Count() Method

We can retrieve the length of a list using its Count attribute:

index.cs

index.cs

copy

              
123456789101112131415161718

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        students.Add("Anna");
        students.Add("Laura");
        students.Add("Jacob");
        students.Add("Aron");

        Console.WriteLine(students[2]);
        Console.WriteLine(students.Count);
    }
}

Dynamic Length

Note that the length of a list is dynamic (changeable), so it changes as we add elements:

index.cs

index.cs

copy

              
1234567891011121314151617181920

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string>();

        Console.WriteLine(students.Count);
        students.Add("Anna");
        Console.WriteLine(students.Count);
        students.Add("Laura");
        Console.WriteLine(students.Count);
        students.Add("Jacob");
        Console.WriteLine(students.Count);
        students.Add("Aron");
        Console.WriteLine(students.Count);
    }
}

Initialization

We can also initialize a list with some elements using the following syntax:

List<dataType> listName = new List<dataType>{ element1, element2, … };

For-example:

index.cs

index.cs

copy

              
12345678910111213141516

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string> { "Anna", "Laura", "Jacob", "Aron" };

        // It is still possible to add additional elements after initialization
        students.Add("Markus"); 

        Console.WriteLine(students.Count);
        Console.WriteLine(students[4]);
    }
}

Looping Through Lists

Looping through a List similar to how we would loop through Arrays

- Using a for-loop:

index.cs

index.cs

copy

              
123456789101112131415

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string> { "Anna", "Laura", "Jacob", "Aron" };

        for (int i = 0; i < students.Count; i++)
        {
            Console.WriteLine(students[i]);
        }
    }
}

- Using a foreach loop

index.cs

index.cs

copy

              
123456789101112131415

            
using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<string> students = new List<string> { "Anna", "Laura", "Jacob", "Aron" };

        foreach (string studentName in students)
        {
            Console.WriteLine(studentName);
        }
    }
}

Tip:

To make the declaration syntax shorter we can also use implicit declaration. To recall, an explicit declaration is when we specify the data type during variable declaration, for-example:

index.cs

index.cs

copy

              
1

            
float number = 7.9f;

On the other hand, in implicit declaration we can simply use the var keyword and the compiler automatically infers the data type of the variable according to the assigned value:

index.cs

index.cs

copy

              
1

            
var number = 7.9f;

We can use implicit declaration when declaring lists as well:

var listName = new List<dataType>();
// or
var listName = new List<dataType>{ element1, element2, … };

For-example:

index.cs

index.cs

copy

              
1

            
var numbers = new List<int> { 1, 2, 3, 4, 5 };

1. What will be the output of the following code:

2. Which module is needed to be imported for using lists?

3. Which method is used for retrieving the size (length) of a list?

question mark

What will be the output of the following code:

Select the correct answer

question mark

Which module is needed to be imported for using lists?

Select the correct answer

question mark

Which method is used for retrieving the size (length) of a list?

Select the correct answer

Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 1. Kapitel 1
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