C#

Introduction

About C#

• C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.
• C# is used to develop web apps, desktop apps, mobile apps, games and much more.
• It is an object-oriented programming language created by Microsoft that runs on the .NET Framework.
• C# has roots from the C family, and the language is close to other popular languages like C++ and Java.
• The first version was released in year 2002. The latest version, C# 12, was released in November 2023.

C# is used for:

• Mobile applications
• Desktop applications
• Web applications
• Web services
• Web sites
• Games
• VR
• Database applications
• And much, much more!

keywords :- 

Access Modifiers

• public
• private
• protected
• internal

Data Types 

• bool
• byte
• char
• decimal
• double
• float
• int
• long
• sbyte
• short
• string
• uint
• ulong
• ushort

Control Flow

• break
• case
• catch
• continue
• default
• do
• else
• finally
• for
• foreach
• goto
• if
• lock
• return
• switch
• throw
• try
• while

Modifiers

• abstract
• async
• const
• event
• extern
• override
• partial
• readonly
• sealed
• static
• unsafe
• virtual
• volatile

Others

• as
• base
• checked
• default
• explicit
• false
• fixed
• implicit
• is
• new
• null
• operator
• sizeof
• stackalloc
• this
• true
• typeof
• unchecked
• void

Class Members

• class
• delegate
• enum
• interface
• namespace
• struct

Method Parameters

• in
• out
• ref
• params

C# Syntax :- 

using System;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            // Use Console class from the System namespace
            Console.WriteLine("Hello World!");
        }
    }
}

Variable: 

variable is a storage location identified by a name that holds data which can be modified during program execution.

• int age;
• string name;

Identifier: 

an identifier is a name used to identify a variable, method, class, or any other user-defined item.

Note: 

Every C# statement ends with a semicolon ;.

Note:

C# is case-sensitive; “MyClass” and “myclass” have different meaning.

C# Output

To output values or print text in C#, you can use the WriteLine() method:

The curly braces {} marks the beginning and the end of a block of code.

C# Comments

Single-line comments start with two forward slashes (//).

Multi-line comments start with /* and ends with */.

C# Data Types

1. Value Types

2. Reference Types

3. Nullable Types

4. Enumerations (enum)

5. Structs

6. Tuples

1. Value Types

• int: 32-bit integer
• double: 64-bit floating-point
• char: 16-bit Unicode character
• bool: Boolean (true/false)
• byte: 8-bit unsigned integer
• short: 16-bit integer
• long: 64-bit integer
• float: 32-bit floating-point
• decimal: 128-bit precise decimal

Syntax Data type:-

• int number = 10;
• float price = 9.99f;
• double total = 100.50;
• char letter = ‘A’;
• string message = “Hello”;
• bool isTrue = true;+

2. Reference Types

Class Types

• Defined using class
• Example: class Person { public string Name; public int Age; }
• Array Types
• Fixed-size or dynamic collection of elements
• Example: int[] numbers = new int[5];

String Type

• Sequence of characters
• Example: string greeting = “Hello, World!”;
• Delegate Types
• Reference to methods
• Example: delegate void Del(string message);

3. Nullable Types

Allow value types to be null

Example: int? nullableInt = null;

4. Enumerations (enum)

Enums are a distinct type that consists of a set of named constants called the enumerator list.

Example:-  enum Days { Sunday, Monday, Tuesday, 

Wednesday, Thursday, Friday, Saturday }

Days today = Days.Monday;

5. Structs

Structs are value types that are typically used to encapsulate small groups of related variables.

Example: struct Point { public int X; public int Y; }

6. Tuples

Tuples are data structures that can store multiple items of different types.

Example:

var person = (Name: “John”, Age: 30);

Console.WriteLine(person.Name);  // Outputs “John”

7. Dynamic Type

The dynamic type bypasses compile-time type checking. This allows for operations that will be resolved at runtime.

dynamic myVar = 1;

myVar = “Hello”; // No compile-time error

Type Casting

Type casting in C# is the process of converting a variable from one type to another. There are two main types of casting in C#: implicit casting and explicit casting.

Implicit Casting :-

Implicit casting is automatically performed by the C# compiler when there is no risk of data loss. This usually happens when converting from a smaller type to a larger type

.

char -> int -> long -> float -> double

Explicit Casting :-

Explicit casting is required when there is a possibility of data loss or when converting from a larger type to a smaller type. This type of casting requires the use of a cast operator.

• double -> float -> long -> int -> char

Arrays

• Arrays are fixed-size collections of elements of the same type.
• Accessed using zero-based index.

Lists

• Arrays are fixed-size collections of elements of the same type.
• Accessed using zero-based index.

When to Use Each:

• Use Arrays when the size is fixed or known.
• Use Lists when flexibility and dynamic resizing are needed.

Interview Questions 

What is C#?

• C# is a modern, object-oriented programming language developed by Microsoft. It is designed for building a variety of applications that run on the .NET Framework.

What is the .NET Framework?

• The .NET Framework is a software framework developed by Microsoft that provides a controlled programming environment where software can be developed, installed, and executed on Windows-based operating systems.

Explain the public, private, protected, and internal access modifiers in C#.

• public: Accessible from any other class.
• private: Accessible only within the class in which it is declared.
• protected: Accessible within its class and by derived class instances.
• internal: Accessible only within files in the same assembly.

What is the difference between a class and an object?

• A class is a blueprint for creating objects, defining the data and behavior that the objects will have. An object is an instance of a class.

What are the pillars of Object-Oriented Programming (OOP)?

• The four pillars of OOP are Encapsulation, Inheritance, Polymorphism, and Abstraction.