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March 03, 2025 00:18
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C# Cheat Sheet

A comprehensive cheat sheet for the C# programming language, covering syntax, data types, control flow, object-oriented programming, and more. This cheat sheet is designed to provide a quick reference for both beginners and experienced C# developers.

Basic Syntax and Data Types

Basic Structure

A basic C# program structure:

using System;

namespace MyNamespace
{
  class MyClass
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Hello, World!");
    }
  }
}

using System;: Imports the System namespace, which contains fundamental classes and base types.
namespace MyNamespace: Declares a namespace to organize code.
class MyClass: Defines a class, the fundamental building block of C# programs.
static void Main(string[] args): The entry point of the program.

Data Types

int

32-bit integer. Example: int age = 30;

float

32-bit floating-point number. Example: float price = 19.99f;

double

64-bit floating-point number. Example: double pi = 3.14159265359;

bool

Boolean value (true or false). Example: bool isAdult = true;

char

Single Unicode character. Example: char grade = 'A';

string

Sequence of characters. Example: string name = "John Doe";

decimal

128-bit data type suitable for financial and monetary calculations. Example: decimal salary = 50000.00m;

Variables

Variable declaration:

dataType variableName = value;

Example:

int age = 30;
string name = "John Doe";

Control Flow

Conditional Statements

if Statement

 
if (condition)
{
  // Code to execute if the condition is true
}

if-else Statement

 
if (condition)
{
  // Code to execute if the condition is true
}
else
{
  // Code to execute if the condition is false
}

if-else if-else Statement

 
if (condition1)
{
  // Code to execute if condition1 is true
}
else if (condition2)
{
  // Code to execute if condition2 is true
}
else
{
  // Code to execute if all conditions are false
}

switch Statement

 
switch (expression)
{
  case value1:
    // Code to execute if expression == value1
    break;
  case value2:
    // Code to execute if expression == value2
    break;
  default:
    // Code to execute if no case matches
    break;
}

Loops

for Loop

 
for (int i = 0; i < 10; i++)
{
  // Code to execute
}

while Loop

 
while (condition)
{
  // Code to execute
}

do-while Loop

 
do
{
  // Code to execute
} while (condition);

foreach Loop

 
foreach (var item in collection)
{
  // Code to execute
}

Jump Statements

break

Terminates the loop or switch statement.

continue

Skips the current iteration of the loop and proceeds to the next iteration.

return

Exits the current method.

goto

Transfers control to a labeled statement (use with caution).

Object-Oriented Programming

Classes and Objects

Class definition:

class MyClass
{
  // Fields (variables)
  // Methods (functions)
}

Object creation:

MyClass obj = new MyClass();

Encapsulation

Access Modifiers

public: Accessible from anywhere.
private: Accessible only within the class.
protected: Accessible within the class and derived classes.
internal: Accessible within the same assembly.
protected internal: Accessible within the same assembly and derived classes.

Properties

Provide controlled access to class fields.

public int Age
{
  get { return age; }
  set { age = value; }
}

Inheritance

Inheritance allows a class to inherit properties and methods from another class.

class DerivedClass : BaseClass
{
  // Additional properties and methods
}

Example:

class Animal
{
  public string Name { get; set; }
  public virtual void MakeSound() { Console.WriteLine("Generic animal sound"); }
}

class Dog : Animal
{
  public override void MakeSound() { Console.WriteLine("Woof!"); }
}

Polymorphism

Virtual Methods

Methods that can be overridden in derived classes.

public virtual void MyMethod() { ... }

Abstract Classes and Methods

Abstract classes cannot be instantiated and may contain abstract methods (methods without implementation).

abstract class MyAbstractClass
{
  public abstract void MyAbstractMethod();
}

Interfaces

Define a contract that classes can implement.

interface IMyInterface
{
  void MyMethod();
}

Advanced Concepts

Delegates and Events

Delegates are type-safe function pointers. Events provide a way for a class to notify other classes when something of interest happens.

delegate void MyDelegate(string message);

event MyDelegate MyEvent;

Example:

public class MyClass
{
  public delegate void MyDelegate(string message);
  public event MyDelegate MyEvent;

  public void DoSomething()
  {
    if (MyEvent != null)
    {
      MyEvent("Something happened!");
    }
  }
}

LINQ (Language Integrated Query)

LINQ provides a unified way to query data from various sources.

var result = from item in collection
             where item.Property > 10
             select item;

Or using method syntax:

var result = collection.Where(item => item.Property > 10);

Asynchronous Programming

async and await

Keywords for writing asynchronous code.

public async Task<int> MyMethodAsync()
{
  await Task.Delay(1000);
  return 42;
}

Task

Represents an asynchronous operation.

Task.Run(() => { ... });

Exception Handling

Exception handling using try-catch blocks.

try
{
  // Code that may throw an exception
}
catch (Exception ex)
{
  // Code to handle the exception
}
finally
{
  // Code that always executes, regardless of exceptions
}