What is C#? 

C# is an object-oriented programming language developed by Microsoft. It is primarily used within the .NET Framework. With C#, you can create applications for Windows, Web, and Mobile platforms. 

• Installing Visual Studio ,

Visual Studio is an Integrated Development Environment (IDE) developed by Microsoft. This IDE is most commonly and successfully used with the C# language. To download and install Visual Studio, visit https://visualstudio.microsoft.com. 

Creating the First Program ,

"Hello World" Program

Let's create this as a Console Application in Visual Studio. 

using System;

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

Code Explanation:

• using System;: This imports the System namespace.

• namespace HelloWorld: Creates a namespace named "HelloWorld".

• class Program: Creates a class named "Program".

• static void Main(string[] args): This is the Main method. It runs first when the program executes.

• Console.WriteLine("Hello World!");: Displays the "Hello World!" message on the console.

Variables and Data Types

You can use variables and data types to store different types of data in C#. Example:

Examples :

int age = 25;       // Integer
double salary = 45500.50;  // Double
char grade = 'A';   // Character
string name = "John";   // String
bool isMarried = false; // Boolean
```

Basic Data Types:

• int: Integer values.

• double: Decimal values.

• char: A single character.

• string: A sequence of characters (text).

• bool: Represents true or false.

Operators

1. Arithmetic Operators:

1- ගණිත කාර්යයන් (Arithmetic Operators)

int x = 10;

int y = 5;

Console.WriteLine(x + y); // Addition

Console.WriteLine(x - y); // Subtraction

Console.WriteLine(x * y); // Multiplication

Console.WriteLine(x / y); // Division

Console.WriteLine(x % y); // Modulus (remainder)
```

2 - Comparison Operators

Console.WriteLine(x == y); // Check if equal

Console.WriteLine(x != y); // Check if not equal

Console.WriteLine(x > y);  // Check if greater

Console.WriteLine(x < y);  // Check if smaller

Console.WriteLine(x >= y); // Check if greater or equal

Console.WriteLine(x <= y); // Check if smaller or equal
```

3 - Logical Operators

bool a = true;
bool b = false;
Console.WriteLine(a && b); // AND
Console.WriteLine(a || b); // OR
Console.WriteLine(!a); // NOT
```

4- Conditional Statements

if  ,

int number = 10;
if (number > 0)
{
Console.WriteLine("Positive Number");
}
```

if-else
if (number > 0)
{
Console.WriteLine("Positive Number");
}
else
{
Console.WriteLine("Non-Positive Number");
}
```

if-else if-else ,

if (number > 0)
{
Console.WriteLine("Positive Number");
}
else if (number < 0)
{
Console.WriteLine("Negative Number");
}
else
{
Console.WriteLine("Zero");
}
```

• Loop Statements ,

for ,

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

while

int j = 1;
while (j <= 5)
{
Console.WriteLine(j);
j++;
}
```

do-while

int k = 1;
do
{
Console.WriteLine(k);
k++;
} while (k <= 5);
```

• Methods ,

1- Basic methods

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

static void Main(string[] args)
{
    Greet(); // Calling the method
}
}
```

2- Methods

class Program
{
static void Greet(string name)
{
    Console.WriteLine("Hello, " + name + "!");
}

static void Main(string[] args)
{
    Greet("John"); // Calling the method
}
}
```

3 - Returning Methods

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

static void Main(string[] args)
{
    int result = Add(5, 3);
    Console.WriteLine(result); // Displaying the result
}
}
```

• Classes and Objects ,

Creating a Class:
class Person
{
public string Name;
public int Age;

public void Introduce()
{
    Console.WriteLine("Hello, my name is " + Name + " and I am " + Age + " years old.");
}
}
```

Creating an Object: 

class Program
{
static void Main(string[] args)
{
    Person person = new Person();
    person.Name = "John";
    person.Age = 30;
    person.Introduce();
}
}
```

Using a Constructor: 

class Person
{
public string Name;
public int Age;

public Person(string name, int age)
{
    Name = name;
    Age = age;
}

public void Introduce()
{
    Console.WriteLine("Hello, my name is " + Name + " and I am " + Age + " years old.");
}
}

class Program
{
static void Main(string[] args)
{
    Person person = new Person("John", 30);
    person.Introduce();
}
}
```

• Inheritance

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

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

class Program
{
static void Main(string[] args)
{
    Dog dog = new Dog();
    dog.Eat();
    dog.Bark();
}
}
```

• Orphism & Interface

Interface ,

interface IAnimal
{
void MakeSound();
}

class Dog : IAnimal
{
public void MakeSound()
{
    Console.WriteLine("Barking...");
}
}

class Cat : IAnimal
{
public void MakeSound()
   

{
    Console.WriteLine("Meowing...");
}
}

class Program
{
static void Main(string[] args)
{
    IAnimal dog = new Dog();
    dog.MakeSound();

     IAnimal cat = new Cat();
    cat.MakeSound();
}
}

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