🧠 C# Fundamentals Every .NET Developer Must Know

Introduction

C# is the heart of the .NET ecosystem. Whether you are building web APIs, desktop apps, or cloud services, everything starts with strong C# fundamentals.

In this article, you’ll learn:

• Core building blocks of C#

• How object-oriented programming works in C#

• Why interfaces are important

• A beginner-friendly introduction to Dependency Injection

This is Week 3 of our .NET weekly blog series.

1️⃣ Variables and Data Types

C# is a strongly typed language, meaning every variable has a specific type.

Common Data Types

int age = 25;
double price = 99.99;
bool isActive = true;
string name = "John";

var Keyword

C# can infer the type automatically:

var count = 10;       // int
var title = "DotNet"; // string

✔ Use var when the type is obvious
❌ Avoid it when readability suffers

2️⃣ Control Flow (Conditions & Loops)

If–Else Statement

if (age >= 18)
{
    Console.WriteLine("Adult");
}
else
{
    Console.WriteLine("Minor");
}

Loops

for (int i = 0; i < 5; i++)
{
    Console.WriteLine(i);
}

foreach (var item in items)
{
    Console.WriteLine(item);
}

3️⃣ Methods (Functions)

Methods help you reuse code and keep it clean.

static int Add(int a, int b)
{
    return a + b;
}

Calling the method:

int result = Add(5, 3);

4️⃣ Classes and Objects (OOP Basics)

C# follows Object-Oriented Programming (OOP).

Creating a Class

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

    public void Greet()
    {
        Console.WriteLine($"Hello, {Name}");
    }
}

Creating an Object

var user = new User
{
    Name = "Alice",
    Age = 30
};

user.Greet();

5️⃣ Interfaces (Why They Matter)

Interfaces define what a class should do, not how it does it.