Kursinnehåll

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?

Class Objects

An object of a class can be created using the following syntax:

index.cs


              1
            
className variableName = new className();

We can access the field of a class using the dot (.) operator:

index.cs


              1
            
variableName.fieldName

For-example:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player p1= new Player();
        
        p1.username = "Don";
        Console.WriteLine(p1.username);
    }
}

The expression new Player(); is used for creating a new object while Player p1 is used for creating a variable for storing that new object. So simply writing Player p1; will only create an empty variable with no object inside it therefore we have to create a new object and, in turn, store it into a variable: Player p1 = new Player();.

Therefore, if we create an Array of size 10 using the Player class, it won't create 10 objects, rather, it will create an empty array with a capacity to store 10 Player objects. This can be understood by the following example:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        
        players[0].username = "Don"; // Error on this line
        Console.WriteLine(players[0].username);
    }
}

The error says "Object reference not set to an instance of an object" which simply means that we are trying to access data from an object that is not there - there is no object to access at the index 0.

This can be fixed by manually creating an object at the index 0:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        players[0] = new Player();
        players[0].username = "Don";
        Console.WriteLine(players[0].username);
    }
}

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 4

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Kursinnehåll

C# Beyond Basics

1. Additional Structures & File Handling

2. Structs & Enumerators

3. Introduction to Object-Oriented Programming (OOP)

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?

Class Objects

An object of a class can be created using the following syntax:

index.cs


              1
            
className variableName = new className();

We can access the field of a class using the dot (.) operator:

index.cs


              1
            
variableName.fieldName

For-example:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player p1= new Player();
        
        p1.username = "Don";
        Console.WriteLine(p1.username);
    }
}

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        
        players[0].username = "Don"; // Error on this line
        Console.WriteLine(players[0].username);
    }
}

This can be fixed by manually creating an object at the index 0:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        players[0] = new Player();
        players[0].username = "Don";
        Console.WriteLine(players[0].username);
    }
}

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 4