INTRODUCTION TO C#

📘 Introduction to C#

✅ What is C#?

C# (C-Sharp) is a modern, object-oriented programming language developed by Microsoft.

👉 It is mainly used to build:

• Desktop applications
• Web applications
• APIs
• Enterprise software

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✅ Why use C#?

• ✔ Simple and easy to learn
• ✔ Strongly typed (reduces errors)
• ✔ Supports Object-Oriented Programming (OOP)
• ✔ Works well with .NET ecosystem
• ✔ Widely used in industry

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❌ Why NOT use C#?

• ❌ Not ideal for low-level system programming (like OS/kernel)
• ❌ Requires .NET runtime
• ❌ Less popular than JavaScript for frontend

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✅ How C# Works (Basic Flow)

1. Write code in .cs file
2. Compile using .NET compiler
3. Run → Output shown in console/app

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📘 Core Concepts Explained

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1️⃣ namespace

✅ What

A namespace is a container for classes.

✅ Why

• Avoids naming conflicts
• Organizes code

✅ Example

namespace MyApp
{
}

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2️⃣ internal

✅ What

An access modifier.

✅ Why

• Restricts access within the same project only

❌ Why not public?

• public exposes it everywhere (less secure)

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3️⃣ class

✅ What

A blueprint for creating objects.

✅ Why

• Groups data and methods together

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4️⃣ object

✅ What

Instance of a class.

✅ Why

• Used to access class properties and methods

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5️⃣ static

✅ What

Belongs to class, not object.

✅ Why

• No need to create object to access it

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6️⃣ void

✅ What

Method returns nothing.

✅ Why

• Used when no return value is needed

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7️⃣ string[]

✅ What

Array of strings.

✅ Why

• Used to store multiple values
• In Main, it stores command-line arguments

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8️⃣ Console.WriteLine()

✅ What

Prints output to console.

✅ Why

• Used for displaying messages

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9️⃣ Console.ReadKey()

✅ What

Waits for a key press.

✅ Why

• Prevents console from closing immediately

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💡 Real-Time Example

👉 Scenario: Display employee details in console

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✅ Full Program with Comments

// Namespace: groups related classes
namespace CompanyApp
{
    // internal: accessible only within this project
    internal class Employee
    {
        // Member variables
        string _name;
        int _age;

        // Method to set values
        public void SetDetails(string name, int age)
        {
            _name = name;
            _age = age;
        }

        // Method to display values
        public void Display()
        {
            Console.WriteLine("Employee Name: " + _name);
            Console.WriteLine("Employee Age: " + _age);
        }
    }

    internal class Program
    {
        // Entry point of program
        static void Main(string[] args) // string[] stores command-line inputs
        {
            // Creating object of Employee class
            Employee emp = new Employee();

            // Setting values
            emp.SetDetails("Rahul", 25);

            // Displaying output
            emp.Display();

            // Static method call (no object needed)
            Console.WriteLine("Press any key to exit...");

            // Wait for user input
            Console.ReadKey();
        }
    }
}

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🔄 Flow of Above Program

1. Program starts → Main()
2. Object emp is created
3. Data is assigned using method
4. Data is displayed
5. Message printed
6. Program waits for key press

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🎯 Key Takeaways

• namespace → organizes code
• internal → restricts access
• class → blueprint
• object → real instance
• static → no object required
• void → no return
• string[] args → input arguments
• Console.WriteLine() → output
• Console.ReadKey() → pause

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✅ One-Line Summary

👉 C# is an object-oriented language where programs are built using classes, objects, and methods, and executed starting from the Main() method.