1. What is C#?

C# (pronounced "C Sharp") is a modern, object-oriented programming language developed by Microsoft. It is commonly used for developing Windows applications, web applications, APIs, desktop software, games and enterprise applications.

C# works closely with the .NET platform. The .NET platform provides libraries, runtime services and tools that allow C# applications to execute and interact with operating systems, databases, networks and other technologies.

Where is C# Used?

• Web application development
• ASP.NET applications
• REST APIs
• Windows desktop applications
• Enterprise software
• Game development using Unity
• Cloud applications

2. Features of C#

C# provides many features that make it suitable for modern software development.

Object-Oriented

C# supports object-oriented programming concepts such as classes, objects, inheritance, encapsulation and polymorphism.

Strongly Typed

C# requires variables to have a specific data type. The compiler checks many type-related errors before the program executes.

Type Safe

C# provides strong type checking which helps prevent invalid operations between incompatible data types.

Automatic Memory Management

C# uses garbage collection to automatically manage memory used by objects.

Rich Library Support

The .NET class libraries provide functionality for collections, files, networking, databases, security and many other operations.

3. C# and .NET

C# is a programming language, while .NET is a development platform that provides the runtime, libraries and tools required to build and execute applications.

4. First C# Program

Let's create a simple C# program that displays "Hello World" on the screen.

using System;

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

Understanding the Program

• using System; imports the System namespace.
• class Program defines a class.
• Main() is the entry point of the application.
• Console.WriteLine() displays text on the console.

5. C# Variables

A variable is a named memory location used to store a value during program execution.

Unlike Python, C# is strongly typed. Therefore, a variable normally has a declared data type.

string name = "Rahul";

int age = 21;

double marks = 85.50;

bool isPassed = true;

Variable Declaration

The general syntax is:

dataType variableName = value;

Example

int number = 100;

Console.WriteLine(number);

6. C# Data Types

A data type specifies the kind of value that a variable can store.

Example

int age = 25;

double salary = 45000.50;

char grade = 'A';

string name = "Student";

bool isActive = true;

7. Constants

A constant is a value that cannot be changed after it has been initialized.

const double PI = 3.14159;

Console.WriteLine(PI);

8. Type Conversion

Type conversion means converting a value from one data type to another.

Implicit Conversion

A smaller compatible numeric type can generally be converted into a larger compatible numeric type automatically.

int number = 100;

double value = number;

Console.WriteLine(value);

Explicit Conversion

double value = 100.75;

int number = (int)value;

Console.WriteLine(number);

9. Arithmetic Operators

Arithmetic operators are used to perform mathematical calculations.

int a = 10;

int b = 3;

Console.WriteLine(a + b);

Console.WriteLine(a - b);

Console.WriteLine(a * b);

Console.WriteLine(a / b);

Console.WriteLine(a % b);

10. Comparison Operators

Comparison operators compare two values and return a Boolean result.

int a = 10;

int b = 20;

Console.WriteLine(a == b);

Console.WriteLine(a != b);

Console.WriteLine(a > b);

Console.WriteLine(a < b);

Console.WriteLine(a >= b);

Console.WriteLine(a <= b);

11. Logical Operators

Logical operators combine Boolean expressions.

int age = 25;

bool result1 = age >= 18 && age <= 60;

bool result2 = age < 18 || age > 60;

bool result3 = !(age > 18);

Console.WriteLine(result1);

Console.WriteLine(result2);

Console.WriteLine(result3);

12. Assignment Operators

int number = 10;

number += 5;

Console.WriteLine(number);

number -= 3;

Console.WriteLine(number);

number *= 2;

Console.WriteLine(number);

13. if / else Statement

Conditional statements allow a program to execute different code depending on a condition.

int age = 20;

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

else-if

int marks = 75;

if (marks >= 90)
{
    Console.WriteLine("Grade A+");
}
else if (marks >= 75)
{
    Console.WriteLine("Grade A");
}
else if (marks >= 60)
{
    Console.WriteLine("Grade B");
}
else
{
    Console.WriteLine("Grade C");
}

14. switch Statement

The switch statement is useful when a program needs to compare one expression against multiple possible values.

int day = 2;

switch (day)
{
    case 1:
        Console.WriteLine("Monday");
        break;

    case 2:
        Console.WriteLine("Tuesday");
        break;

    case 3:
        Console.WriteLine("Wednesday");
        break;

    default:
        Console.WriteLine("Invalid Day");
        break;
}

15. for Loop

A for loop is used when a block of code needs to execute repeatedly for a known or controlled number of iterations.

for (int i = 1; i <= 5; i++)
{
    Console.WriteLine(i);
}

16. while Loop

The while loop executes a block of code while a condition remains true.

int i = 1;

while (i <= 5)
{
    Console.WriteLine(i);

    i++;
}

17. break and continue

break

The break statement terminates the loop immediately.

for (int i = 1; i <= 10; i++)
{
    if (i == 5)
    {
        break;
    }

    Console.WriteLine(i);
}

continue

The continue statement skips the current iteration.

for (int i = 1; i <= 5; i++)
{
    if (i == 3)
    {
        continue;
    }

    Console.WriteLine(i);
}

18. Methods

A method is a reusable block of code that performs a specific task.

static void Greet()
{
    Console.WriteLine("Hello Student");
}

static void Main()
{
    Greet();
}

19. Method Parameters

Parameters allow a method to receive values from the calling code.

static void Add(int a, int b)
{
    int result = a + b;

    Console.WriteLine(result);
}

static void Main()
{
    Add(10, 20);
}

20. Return Values

A method can return a value using the return keyword.

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

static void Main()
{
    int result = Add(10, 20);

    Console.WriteLine(result);
}

21. Method Overloading

Method overloading allows multiple methods to have the same name but different parameter lists.

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

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

static void Main()
{
    Console.WriteLine(Add(10, 20));

    Console.WriteLine(Add(10, 20, 30));
}

22. Classes

A class is a blueprint or template used to create objects. It can contain fields, properties and methods.

class Student
{
    public string Name;

    public void Display()
    {
        Console.WriteLine(Name);
    }
}

23. Objects

An object is an instance of a class.

Student student = new Student();

student.Name = "Rahul";

student.Display();

24. Constructors

A constructor is a special method that is called automatically when an object is created.

class Student
{
    public string Name;

    public Student(string name)
    {
        Name = name;
    }

    public void Display()
    {
        Console.WriteLine(Name);
    }
}

Student student = new Student("Rahul");

student.Display();

25. Encapsulation

Encapsulation means combining data and methods inside a class while controlling how that data can be accessed.

class BankAccount
{
    private double balance;

    public void Deposit(double amount)
    {
        balance += amount;
    }

    public double GetBalance()
    {
        return balance;
    }
}

BankAccount account = new BankAccount();

account.Deposit(5000);

Console.WriteLine(account.GetBalance());

26. Inheritance

Inheritance allows a derived class to reuse members of a base class.

class Animal
{
    public void Eat()
    {
        Console.WriteLine("Animal is eating");
    }
}

class Dog : Animal
{
    public void Bark()
    {
        Console.WriteLine("Dog is barking");
    }
}

Dog dog = new Dog();

dog.Eat();

dog.Bark();

27. Polymorphism

Polymorphism allows the same method or interface to behave differently depending on the object.

class Animal
{
    public virtual void Sound()
    {
        Console.WriteLine("Animal sound");
    }
}

class Dog : Animal
{
    public override void Sound()
    {
        Console.WriteLine("Dog barks");
    }
}

Animal animal = new Dog();

animal.Sound();

28. Arrays

An array stores multiple values of the same data type in a fixed-size collection.

int[] marks = { 80, 75, 90, 85 };

for (int i = 0; i < marks.Length; i++)
{
    Console.WriteLine(marks[i]);
}

29. Collections

Collections provide flexible ways to store and manipulate groups of objects.

List

using System.Collections.Generic;

List<string> students = new List<string>();

students.Add("Amit");

students.Add("Rahul");

students.Add("Priya");

foreach (string student in students)
{
    Console.WriteLine(student);
}

30. Exception Handling

Exception handling allows a program to handle runtime errors gracefully.

try
{
    int a = 10;

    int b = 0;

    int result = a / b;

    Console.WriteLine(result);
}
catch (DivideByZeroException)
{
    Console.WriteLine("Cannot divide by zero.");
}
finally
{
    Console.WriteLine("Program completed.");
}

Keywords

• try contains code that may generate an exception.
• catch handles the exception.
• finally executes after the try/catch block.

31. File Handling

C# provides classes such as File and StreamReader for working with files.

Writing to a File

using System.IO;

File.WriteAllText(
    "student.txt",
    "Welcome to C# Programming"
);

Reading from a File

string content =
    File.ReadAllText("student.txt");

Console.WriteLine(content);

32. C# Mini Project

Student Result Calculator

Let's combine variables, arrays, loops, methods and conditional statements to create a simple student result calculator.

using System;

class Program
{
    static void Main()
    {
        Console.Write("Enter Student Name: ");

        string name = Console.ReadLine();

        int[] marks = new int[3];

        int total = 0;

        for (int i = 0; i < 3; i++)
        {
            Console.Write("Enter marks: ");

            marks[i] = Convert.ToInt32(
                Console.ReadLine()
            );

            total += marks[i];
        }

        double percentage = total / 3.0;

        Console.WriteLine();
        Console.WriteLine("Student Name: " + name);
        Console.WriteLine("Total Marks: " + total);
        Console.WriteLine("Percentage: " + percentage);

        if (percentage >= 75)
        {
            Console.WriteLine("Grade: A");
        }
        else if (percentage >= 60)
        {
            Console.WriteLine("Grade: B");
        }
        else if (percentage >= 50)
        {
            Console.WriteLine("Grade: C");
        }
        else
        {
            Console.WriteLine("Grade: D");
        }
    }
}

Concepts Used

• Variables
• String input
• Arrays
• for loop
• Arithmetic operations
• Conditional statements
• Type conversion

C# Course Summary

You have now covered the major fundamentals required to begin programming with C#. The next step is to practice each concept by building small applications.

Topics Covered

• Introduction to C#
• Features of C#
• C# and .NET
• Variables and Data Types
• Constants and Type Conversion
• Operators
• Conditional Statements
• Loops
• Methods
• Method Parameters and Return Values
• Method Overloading
• Classes and Objects
• Constructors
• Encapsulation
• Inheritance
• Polymorphism
• Arrays
• Collections
• Exception Handling
• File Handling
• Mini Project