C# Classes and Objects Explained

Classes and objects are fundamental concepts in C# and object-oriented programming. A class defines the structure and behavior of an object, while an object is an instance created from that class.

What is a Class in C#?

A class is a blueprint that defines data and behavior. It can contain fields, properties, methods, constructors, and other members.

class Car
{
    public string Brand { get; set; }
    public int Year { get; set; }

    public void Start()
    {
        Console.WriteLine("Car started");
    }
}

What is an Object?

An object is an instance of a class. When an object is created, it can store its own values for the properties and use the methods defined by the class.

Car car = new Car();
car.Brand = "Toyota";
car.Year = 2025;

car.Start();

Class vs Object

C# Properties

Properties provide a convenient way to expose and control data stored by an object.

class Student
{
    public string Name { get; set; }
    public int Age { get; set; }
}

Creating Multiple Objects

A single class can be used to create many objects. Each object can contain different property values.

Student student1 = new Student();
student1.Name = "Alice";
student1.Age = 20;

Student student2 = new Student();
student2.Name = "Bob";
student2.Age = 22;

Methods in a Class

Methods define actions that an object can perform. They help keep related behavior together with the data it operates on.

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

Calculator calculator = new Calculator();
int result = calculator.Add(10, 20);

Constructors in C#

A constructor is a special method that runs when an object is created. Constructors are commonly used to initialize object properties.

class Product
{
    public string Name { get; set; }
    public double Price { get; set; }

    public Product(string name, double price)
    {
        Name = name;
        Price = price;
    }
}

Product product = new Product("Laptop", 75000);

Access Modifiers

Access modifiers control where classes and their members can be accessed.

• public allows access from other code
• private restricts access to the containing type
• protected allows access within the type and derived types
• internal allows access within the same assembly

Common C# Class Members

Example C# Class

class Employee
{
    public string Name { get; set; }
    public double Salary { get; set; }

    public Employee(string name, double salary)
    {
        Name = name;
        Salary = salary;
    }

    public void DisplayInfo()
    {
        Console.WriteLine($"Name: {Name}");
        Console.WriteLine($"Salary: {Salary}");
    }
}

Employee employee = new Employee("John", 50000);
employee.DisplayInfo();

Real-World Applications

• User classes in web applications
• Product classes in e-commerce systems
• Employee models in business applications
• Customer objects in banking systems
• Game objects in C# game development

Common Mistakes to Avoid

• Creating classes without clear responsibilities
• Making every member public unnecessarily
• Duplicating code instead of using reusable methods
• Ignoring constructors when initialization is required
• Putting unrelated functionality into one class

Advanced C# OOP Concepts

• Inheritance
• Encapsulation
• Polymorphism
• Abstraction
• Interfaces
• Records
• Generics

Practice Exercises

• Create a Book class
• Add title and author properties
• Create a constructor
• Add a method to display book information
• Create multiple Book objects
• Create a simple BankAccount class

Conclusion

Classes and objects form the foundation of object-oriented programming in C#. By learning how to define classes, create objects, use properties, write methods, and initialize objects with constructors, you can build reusable and maintainable C# applications.