🏠 Building Your First C# Home

Imagine you’re building a house. You need a blueprint, rooms, and a way to talk to visitors. C# works the same way!

🎬 The Story Begins

Once upon a time, there was a builder named C# (pronounced “C-Sharp”). This builder was famous for creating amazing digital houses called programs. Today, you’ll learn how C# builds these houses from the ground up!

🏗️ Program Structure: The Blueprint

Every house needs a blueprint. In C#, the blueprint looks like this:

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Hello!");
    }
}

Think of it like this:

• using System; = Bringing your toolbox
• class Program = The house name
• static void Main() = The front door (where everything starts!)

🚪 The Main Door

The Main method is special. It’s the front door of your program. When you run your program, C# always looks for this door first!

static void Main()
{
    // Your code starts here
}

📦 Variables: The Storage Boxes

Imagine you have boxes in your house to store things. Variables are those boxes!

string name = "Alex";
int age = 10;

Breaking it down:

• string = A box for words (text)
• int = A box for whole numbers
• name and age = Labels on your boxes
• "Alex" and 10 = What’s inside!

🔒 Constants: Locked Boxes

Some boxes should never change. Like your birthday - it’s always the same!

const int BirthYear = 2015;

The const keyword means “this box is locked forever!”

🧱 Primitive Data Types: Different Box Sizes

Just like you use small boxes for jewelry and big boxes for toys, C# has different box types:

int score = 100;
double price = 9.99;
bool isHappy = true;
char grade = 'A';
string message = "Great job!";

🔮 Type Inference with var: The Smart Box

Sometimes C# is so smart, it can guess what type of box you need!

var fruit = "Apple";  // C# knows it's a string
var count = 5;        // C# knows it's an int
var cost = 2.50;      // C# knows it's a double

The magic word var tells C#: “You figure out the box type!”

⚠️ Important: You must put something in the box right away when using var. C# needs to see what’s inside to know the type!

📺 Console Input and Output: Talking to Users

Your program can talk to people and listen to them too!

📢 Speaking Out (Output)

Console.WriteLine("Hello, friend!");
Console.Write("Same line... ");
Console.Write("still same line!");

• WriteLine = Say something, then go to new line
• Write = Say something, stay on same line

👂 Listening In (Input)

Console.Write("What's your name? ");
string name = Console.ReadLine();
Console.WriteLine("Hi, " + name + "!");

ReadLine() waits for someone to type and press Enter!

✨ Top-Level Statements: The Quick Start

Modern C# has a shortcut! Instead of writing all that blueprint stuff, you can just start coding:

The old way:

using System;
class Program
{
    static void Main()
    {
        Console.WriteLine("Hi!");
    }
}

The new way (top-level):

Console.WriteLine("Hi!");

That’s it! Just one line! C# handles the blueprint automatically.

➕ Basic Operators: The Math Tools

C# can do math and comparisons for you!

🔢 Math Operators

int a = 10;
int b = 3;

int sum = a + b;      // 13 (addition)
int diff = a - b;     // 7 (subtraction)
int product = a * b;  // 30 (multiplication)
int quotient = a / b; // 3 (division)
int remain = a % b;   // 1 (remainder)

⚖️ Comparison Operators

bool isEqual = (5 == 5);   // true
bool notEqual = (5 != 3);  // true
bool greater = (5 > 3);    // true
bool less = (3 < 5);       // true

🔗 Logical Operators

bool both = true && true;   // AND: both must be true
bool either = true || false; // OR: one must be true
bool opposite = !true;       // NOT: flips the value

🌫️ Null Operators: Handling Empty Boxes

Sometimes a box might be empty (null). C# has special tools to handle this safely!

❓ The ? Operator (Nullable Types)

int? mysteryNumber = null;  // This box CAN be empty

The ? after the type means “this could be empty!”

?? The Null-Coalescing Operator

string name = null;
string display = name ?? "Unknown";
// If name is empty, use "Unknown" instead

Think of ?? as saying: “Use this, OR if it’s empty, use that instead!”

??= The Null-Coalescing Assignment

string message = null;
message ??= "Default";
// Only fills the box if it's empty

?. The Null-Conditional Operator

string name = null;
int? length = name?.Length;
// If name is null, don't crash - just return null

The ?. is like asking: “If this exists, then do this… if not, never mind!”

🎯 Quick Summary

graph LR
    A[🏠 C# Program] --> B[📋 Structure]
    A --> C[📦 Variables]
    A --> D[📺 Console I/O]
    A --> E[➕ Operators]

    B --> B1[Main Method]
    B --> B2[Top-Level Statements]

    C --> C1[Primitive Types]
    C --> C2[var Keyword]
    C --> C3[Constants]

    D --> D1[WriteLine/Write]
    D --> D2[ReadLine]

    E --> E1[Math: + - * / %]
    E --> E2[Comparison: == != > <]
    E --> E3[Null: ?? ?. ??=]

🎉 You Did It!

You just learned the foundations of C#! You now know how to:

• ✅ Write a program structure
• ✅ Create variables and constants
• ✅ Use different data types
• ✅ Let C# guess types with var
• ✅ Talk to users with Console
• ✅ Use the modern top-level shortcut
• ✅ Do math and comparisons
• ✅ Handle empty boxes with null operators

You’re now ready to build amazing things with C#! 🚀

Remember: Every expert was once a beginner. Keep building, keep learning!