Classes & Objects

Syntax

public class ClassName {\n  // fields, properties, methods\n}

Examples

public class Person
{
    public string Name;
    public int Age;

    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }

    public void Introduce()
    {
        Console.WriteLine($"Hi, I'm {Name} and I'm {Age} years old.");
    }
}

// Usage
Person person = new Person("Alice", 25);
person.Introduce();

Person alice = new Person("Alice", 25);
Person bob = new Person("Bob", 30);

alice.Age = 26;  // only affects alice, not bob

Console.WriteLine($"{alice.Name}: {alice.Age}");  // Alice: 26
Console.WriteLine($"{bob.Name}: {bob.Age}");        // Bob: 30

public class Counter
{
    private static int count = 0;  // shared across all instances
    public int InstanceId;

    public Counter()
    {
        count++;
        InstanceId = count;
    }

    public static int GetCount() => count;
}

Counter c1 = new Counter();
Counter c2 = new Counter();
Counter c3 = new Counter();

Console.WriteLine($"Total instances: {Counter.GetCount()}");  // 3
Console.WriteLine($"c2 ID: {c2.InstanceId}");                   // 2

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

Product laptop = new Product
{
    Name = "Laptop",
    Price = 999.99
};

Console.WriteLine($"{laptop.Name}: ${laptop.Price}");

Best practices

• Use meaningful, PascalCase class names that describe what the class represents (Customer, not customer or CustomerClass)
• Prefer properties (get/set) over public fields for exposing data - it gives you a way to add validation later without breaking callers
• Write one class per file, with the filename matching the public class name, matching standard C# project conventions
• Follow the Single Responsibility Principle - each class should have one clear, well-defined purpose

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation