Master C# Programming From Scratch

1. Exception Handling

Exception handling is used to handle runtime errors in a program without terminating the application unexpectedly.

Why Do We Need Exception Handling?

• Prevents application crashes.
• Provides meaningful error messages.
• Allows the application to continue safely.
• Helps developers identify runtime problems.
• Improves application reliability.

try-catch

The try block contains code that may generate an exception. The catch block handles the exception.

using System;
 
try
{
    int a = 10;
    int b = 0;

    int result = a / b;

    Console.WriteLine(result);
}
catch (Exception ex)
{
    Console.WriteLine("An error occurred.");
}

Output

An error occurred.

Displaying Exception Message

using System;
 
try
{
    int number = int.Parse("ABC");
}
catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

Output

The input string 'ABC' was not in a correct format.

Multiple catch Blocks

Multiple catch blocks can be used to handle different types of exceptions separately.

using System;
try
{
    int[] numbers = { 10, 20, 30 };

    Console.WriteLine(numbers[5]);
}
catch (IndexOutOfRangeException)
{
    Console.WriteLine("Invalid array index.");
}
catch (Exception)
{
    Console.WriteLine("Some other error occurred.");
}

Output

Invalid array index.

finally Block

The finally block executes whether an exception occurs or not. It is commonly used for cleanup operations.

using System;
 
try
{
    Console.WriteLine("Try block executed.");
}
catch
{
    Console.WriteLine("Catch block executed.");
}
finally
{
    Console.WriteLine("Finally block executed.");
}

Output

Try block executed.
Finally block executed.

throw Keyword

The throw keyword is used to explicitly generate an exception.

using System;
 
int age = 15;

if (age < 18)
{
    throw new Exception("Age must be 18 or above.");
}

2. Delegates and Events

Delegates and events provide a mechanism for passing methods as values and creating event-driven applications.

What is a Delegate?

A delegate is a type-safe reference to a method. It can store a reference to a method and invoke that method later.

using System;
 
delegate void MessageDelegate();

class Program
{
    static void ShowMessage()
    {
        Console.WriteLine("Welcome to C#");
    }

    static void Main()
    {
        MessageDelegate message = ShowMessage;

        message();
    }
}

Output

Welcome to C#

Delegate with Parameters

using System;
 
delegate void CalculateDelegate(int a, int b);

class Program
{
    static void Add(int a, int b)
    {
        Console.WriteLine(a + b);
    }

    static void Main()
    {
        CalculateDelegate calculate = Add;

        calculate(10, 20);
    }
}

Output

30

What is an Event?

An event is used to notify other parts of an application when something happens.

Examples include button clicks, payment completion, order placement, and user registration.

Event Example

using System;
 
class Order
{
    public event Action OrderPlaced;

    public void PlaceOrder()
    {
        Console.WriteLine("Order placed.");

        OrderPlaced?.Invoke();
    }
}

class Program
{
    static void Main()
    {
        Order order = new Order();

        order.OrderPlaced += SendNotification;

        order.PlaceOrder();
    }

    static void SendNotification()
    {
        Console.WriteLine("Notification sent.");
    }
}

Output

Order placed.
Notification sent.

3. Lambda Expressions

Lambda expressions provide a short and readable syntax for writing anonymous functions.

Lambda Syntax

(parameters) => expression

Simple Lambda Example

using System;
 
Func<int, int> square = number => number * number;

Console.WriteLine(square(5));

Output

25

Lambda with Multiple Parameters

using System;
 
Func<int, int, int> add =
    (a, b) => a + b;

Console.WriteLine(add(10, 20));

Output

30

Lambda with List

using System;
using System.Collections.Generic;

namespace ListExample
{
    class Program
    {
        static void Main()
        {
            List numbers =
                new List { 10, 20, 30, 40, 50 };

            numbers.ForEach(number =>
                Console.WriteLine(number));
        }
    }
}

Output

10
20
30
40
50

4. Extension Methods

Extension methods allow developers to add new methods to an existing type without modifying the original type or creating a derived class.

Extension Method Syntax

An extension method is defined inside a static class. The first parameter uses the this keyword.

public static class StringExtensions
{
    public static bool IsLong(this string text)
    {
        return text.Length > 5;
    }
}

Extension Method Example

using System;
 
public static class StringExtensions
{
    public static bool IsLong(this string text)
    {
        return text.Length > 5;
    }
}

class Program
{
    static void Main()
    {
        string name = "Rahul";

        Console.WriteLine(name.IsLong());
    }
}

Output

False

Another Extension Method Example

using System;
 
public static class NumberExtensions
{
    public static bool IsEven(this int number)
    {
        return number % 2 == 0;
    }
}

class Program
{
    static void Main()
    {
        int number = 20;

        Console.WriteLine(number.IsEven());
    }
}

Output

True

5. LINQ

LINQ stands for Language Integrated Query. It provides a consistent way to query and manipulate data from collections, databases, XML and other data sources.

Why Do We Use LINQ?

• Filter data easily.
• Sort collections.
• Search for records.
• Select specific fields.
• Group data.
• Calculate values such as Sum and Average.
• Write readable data-processing code.

Where() Method

Where() is used to filter data based on a condition.

using System;
 
List<int> numbers =
    new List<int> { 10, 15, 20, 25, 30 };

var result = numbers.Where(n => n > 20);

foreach (int number in result)
{
    Console.WriteLine(number);
}

Output

25
30

Select() Method

Select() is used to transform or project each element.

using System;
 
List<int> numbers =
    new List<int> { 1, 2, 3, 4, 5 };

var squares = numbers.Select(n => n * n);

foreach (int number in squares)
{
    Console.WriteLine(number);
}

Output

1
4
9
16
25

OrderBy()

OrderBy() sorts data in ascending order.

using System;
 
List<int> numbers =
    new List<int> { 50, 20, 40, 10, 30 };

var result = numbers.OrderBy(n => n);

foreach (int number in result)
{
    Console.WriteLine(number);
}

Output

10
20
30
40
50

OrderByDescending()

using System;
 
List<int> numbers =
    new List<int> { 10, 40, 20, 50, 30 };

var result = numbers.OrderByDescending(n => n);

foreach (int number in result)
{
    Console.WriteLine(number);
}

Output

50
40
30
20
10

First() and FirstOrDefault()

First() returns the first element of a collection. FirstOrDefault() returns the first element or the default value when no matching element exists.

using System;
 
List<string> names =
    new List<string> { "Rahul", "Sneha", "Amit" };

string firstName = names.First();

Console.WriteLine(firstName);

Output

Rahul

Any() Method

Any() checks whether at least one element satisfies a specified condition.

using System;
 
List<int> numbers =
    new List<int> { 10, 20, 30, 40 };

bool result = numbers.Any(n => n > 25);

Console.WriteLine(result);

Output

True

Count() Method

using System;
 
List<int> numbers =
    new List<int> { 10, 20, 30, 40, 50 };

int count = numbers.Count();

Console.WriteLine(count);

Output

5

Sum() and Average()

using System;
 
List<int> marks =
    new List<int> { 80, 90, 70, 85, 75 };

int total = marks.Sum();
double average = marks.Average();

Console.WriteLine("Total: " + total);
Console.WriteLine("Average: " + average);

Output

Total: 400
Average: 80

LINQ Method Summary