Module 1: Programming Fundamentals (C# Basics)

1. What is .NET & Why Enterprises Use It?

At its simplest, .NET (pronounced “dot net”) is a free, open-source, cross-platform developer platform for building many different types of applications. It provides a programming model, a comprehensive software library, and a runtime environment.

The Ecosystem Components

The Runtime: Think of this as the “engine.” It’s the virtual machine that manages the execution of programs (handling memory, security, and hardware interaction).
The Libraries: A massive collection of pre-written code (APIs) that developers use so they don’t have to “reinvent the wheel” for things like reading files, sending emails, or processing JSON.
The Languages: .NET supports C# (the most popular), F# (functional), and VB.NET (legacy).

Why Enterprises Choose .NET

Enterprises (large corporations) don’t just pick tools because they are “cool”; they pick them for stability and ROI (Return on Investment).

Security: It has built-in features to prevent common attacks like SQL injection and Cross-Site Scripting (XSS).
Scalability: It can handle millions of requests, which is why companies like UPS, Stack Overflow, and Microsoft use it.
Microsoft Support: Large companies feel safe knowing a trillion-dollar company is maintaining the ecosystem.
Productivity: With “NuGet” (the package manager) and powerful IDEs, developers can build complex systems much faster than in many other languages.

2. .NET Framework vs. .NET Core vs. .NET 8+

This is the most confusing part for beginners because of the naming history. Here is the breakdown:

Feature	.NET Framework	.NET Core	.NET 5, 6, 7, 8+
Era	2002 – 2019	2016 – 2020	2020 – Present
OS	Windows Only	Windows, macOS, Linux	Cross-platform
Status	Legacy (Maintenance)	Replaced by .NET 5+	The Current Standard
Performance	Good	Excellent	Top-tier / Blazing Fast

Detailed Breakdown

.NET Framework: The original version. It’s tied to the Windows Operating System. If you are maintaining an old bank application built in 2010, you are likely using this.
.NET Core: A complete rewrite. Microsoft realized the world was moving to Linux servers and Cloud (AWS/Azure). They made it lightweight, modular, and fast.
.NET 5, 6, 7, 8+: Microsoft dropped the word “Core.” These versions represent the “Unity” of the platform. .NET 8 is a Long Term Support (LTS) version, meaning it is the most stable and recommended version for modern enterprise work today.

3. Setting Up: Visual Studio vs. VS Code

You need a place to write your code (an Integrated Development Environment or IDE).

Visual Studio (The “Heavyweight Champion”)

What it is: A full-featured IDE.
Best for: Large enterprise projects, complex debugging, and desktop (WPF/WinForms) apps.
Pros: It does everything for you. It has the best “intellisense” (code completion) and visual designers.
Cons: It’s a massive download (gigabytes) and can be slow on older computers.

VS Code (The “Lightweight Ninja”)

What it is: A code editor.
Best for: Web development, cross-platform work, and people who like a fast, minimalist interface.
Pros: Extremely fast, works on everything, and has a huge library of plugins.
Cons: You have to manually install extensions (like the “C# Dev Kit”) to make it work like a full IDE.

4. Writing Your First C# Program

Let’s look at the “Hello World” code and explain every single word, as this is where the magic starts.

using System;

namespace HelloWorldApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");
        }
    }
}

Breaking Down the Terms:

using System;: This is a Namespace Import. It tells the computer, “I want to use the standard ‘System’ library which contains basic functions like printing text.”
namespace HelloWorldApp: This is a container used to organize your code. It prevents “name collisions” (e.g., if two people name a class “User”, the namespace keeps them separate).
class Program: C# is an Object-Oriented language. Everything happens inside a class. Think of a class as a blueprint for a building.
static: This means the method belongs to the class itself, not a specific “instance” of the class. You don’t need to “create” a program to run it.
void: This is the Return Type. It means “this function does its job and returns nothing back.”
Main: This is the Entry Point. When you click “Run,” the computer specifically looks for a folder called Main. If it doesn’t find it, the app won’t start.
string[] args: This allows you to pass information into your app when you start it from a command line.
Console.WriteLine: This is the command to print text to the screen.

How the Code Actually Runs

When you hit “Run,” a two-step process occurs:

Compilation: Your C# code is turned into Intermediate Language (IL). It’s not quite machine code yet.
JIT (Just-In-Time) Compilation: When the app runs, the CLR (Common Language Runtime) converts that IL into the specific machine code your CPU understands.

1. Variables & Data Types

In C#, a variable is a reserved memory location to store values. Because C# is a strongly typed language, you must tell the compiler exactly what kind of data you are storing.

Simple (Value) Types

These store the actual data in a part of memory called the Stack.

int: Stores whole numbers (integers) from -2.1 billion to +2.1 billion.
long: For much larger whole numbers (64-bit).
double / decimal: Used for fractional numbers. Tip: In enterprise finance apps, we use decimal because it has higher precision for money.
bool: Short for Boolean; stores only true or false.
char: Stores a single character, like 'A', wrapped in single quotes.

Complex (Reference) Types

These store a “pointer” to a location in a memory area called the Heap.

string: A sequence of characters, like "Hello", wrapped in double quotes.
object: The “Grandparent” of all types in .NET. It can hold anything, but it’s slower to use.

2. Operators & Expressions

Operators are symbols used to perform operations on variables.

Arithmetic Operators: +, -, *, /, and % (Modulus—returns the remainder of a division).
Comparison Operators: == (is equal to), != (not equal), >, <, >=, <=. These always result in a bool.
Logical Operators: * && (AND): True if both sides are true.
- || (OR): True if at least one side is true.
- ! (NOT): Reverses the result.
Assignment Operators: = (assigns a value), += (adds and assigns), ++ (increments by 1).

3. Conditional Statements (Control Flow)

Logic allows your program to make decisions. Without these, a program would just be a list of instructions running in a straight line.

If / Else If / Else

The most common way to branch logic.

int age = 18;
if (age >= 21) {
    Console.WriteLine("Entry permitted.");
} else if (age >= 18) {
    Console.WriteLine("Entry permitted with restrictions.");
} else {
    Console.WriteLine("Entry denied.");
}

Switch Statement

Used when you have many fixed options for a single variable. It is cleaner and faster than writing ten if statements.

string day = "Monday";
switch (day) {
    case "Monday": Console.WriteLine("Back to work!"); break;
    case "Friday": Console.WriteLine("Weekend is near!"); break;
    default: Console.WriteLine("Just another day."); break;
}

4. Loops (Iteration)

Loops allow you to repeat a block of code multiple times. This is essential for processing lists of data.

for Loop: Used when you know exactly how many times you want to repeat (e.g., “Do this 10 times”).C#for (int i = 0; i < 5; i++) { Console.WriteLine("Iteration: " + i); }
while Loop: Used when you don’t know how many times it will run; it keeps going as long as the condition is true.
do-while Loop: Similar to while, but it guarantees the code runs at least once before checking the condition.
foreach Loop: The “Enterprise King.” It is the safest and most readable way to go through every item in a collection (like a list of employees).

5. Console Applications

In the modern era of fancy web apps and mobile games, why do we start with Console Applications?

Zero Distractions: There is no HTML, CSS, or UI logic. You focus 100% on the C# logic.
The “Brains”: Most enterprise background tasks (Microservices, Web Jobs, Data Migrators) are essentially Console Apps that run on a server without a screen.
Input/Output (I/O):
- Console.WriteLine(): Sends data to the user.
- Console.ReadLine(): Pauses the program and waits for the user to type something and hit Enter.

Putting it all together

Here is a “mini-program” using everything above:

Console.WriteLine("Enter your score (0-100):");
string input = Console.ReadLine();
int score = int.Parse(input); // Converting string to number

if (score >= 50) {
    for (int i = 0; i < 3; i++) {
        Console.WriteLine("You Passed!");
    }
} else {
    Console.WriteLine("Try again next time.");
}

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