Зміст курсу

C# Beyond Basics

1. Additional Structures & File Handling

What are Lists?Practicing List Declaration List Methods What are Dictionaries?Practicing Dictionaries Reading Files using StreamReader Reading Files using File Methods Writing Files Error Handling Practicing Error Handling

2. Structs & Enumerators

What are Structs?Defining & Using a Structure Practicing Structs Structs with Other Data Structures Struct Methods Correctly Accessing Fields in Struct Methods Practicing Methods Struct Constructors Practicing Constructors Enumerators Practicing Enumerator

3. Introduction to Object-Oriented Programming (OOP)

What is Object-Oriented Programming?Defining Classes Practice: Creating Classes Class Objects Class Objects vs Struct Objects Practice: Objects Class Methods Practice: Methods Class Constructors Practice: Constructors

4. OOP Essentials

Derived Classes Derived Classes Practice Common Access Modifiers Access Modifiers Practice The `static` Keyword Practicing `static` Keyword Method Overloading Method Overloading Practice

5. OOP Principles

What are the Principles of OOP?Inheritance Practicing Inheritance Polymorphism Practicing Polymorphism Encapsulation Encapsulation Practice Abstraction Abstraction Practice What's Next?

What 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


              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:

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              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:

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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


              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:

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              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


              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:

For-example:

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              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:

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              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

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              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:

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              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:

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              1
            
var number = 7.9f;

We can use implicit declaration when declaring lists as well:

For-example:

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

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