C# Cheat Sheet — Quick Reference Guide for Developers

C# (C-Sharp) is a modern, object-oriented programming language developed by Microsoft. It runs on the .NET framework and is widely used for building desktop apps, web apps, games, and enterprise software.

This C# Cheatsheet gives you a quick and complete overview of all major topics — from basic syntax to advanced OOP and LINQ — with easy-to-understand examples for practical learning.

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C# Basics for Beginners

Concept	Description	Example
File Extension	.cs	Program.cs
Namespace	Organizes classes	namespace DemoApp { }
Entry Point	Main method	static void Main()
Comments	Single or multi-line	// Comment or /* Comment */

Example:

using System;

namespace HelloWorld {
    class Program {
        static void Main() {
            Console.WriteLine("Hello, C#!");
        }
    }
}

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Data Types in C#

Type	Keyword	Size (bytes)	Example
Integer	int	4	int age = 25;
Floating-point	float, double, decimal	4 / 8 / 16	float price = 12.5F;
Character	char	2	char grade = 'A';
Boolean	bool	1	bool isValid = true;
String	string	Variable	string name = "John";
Object	object	Any type	object data = 42;

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C# Variables and Constants

int x = 10;
const double PI = 3.1416;
var message = "Hello!";

• var allows type inference at compile time.
• const defines immutable values.

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Operators in C#

Category	Operators	Example
Arithmetic	+ - * / %	x + y
Relational	== != > < >= <=	if(a > b)
Logical	`&&
Assignment	= += -= *= /=	x += 5;
Conditional	?:	result = (a > b) ? a : b;
Null-Coalescing	??	value = name ?? "Guest";

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Conditional Statements in C#

if (x > 0)
    Console.WriteLine("Positive");
else if (x < 0)
    Console.WriteLine("Negative");
else
    Console.WriteLine("Zero");

Switch Example:

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

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Loops in C#

Type	Syntax	Example
for	for(init; condition; increment)	for(int i=0;i<5;i++)
while	while(condition)	while(i<10)
do-while	do { } while(condition);	Executes once
foreach	foreach(var item in collection)	Loops through arrays or lists

Example:

foreach (int n in new int[]{1,2,3})
    Console.WriteLine(n);

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C# Functions (Methods)

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

• Static Methods: Belong to the class, not instance.
• Overloading: Same name, different parameters.
• Default Parameters: void Greet(string name="User").

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C# Object-Oriented Programming (OOP)

Concept	Definition	Example
Class	Blueprint for objects	class Car { }
Object	Instance of class	Car myCar = new Car();
Encapsulation	Data hiding via access modifiers	private int age;
Inheritance	Reusing base class	class Child : Parent
Polymorphism	Method overriding	virtual and override
Abstraction	Hiding complexity	abstract class Shape {}

Example:

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

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

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C# Collections

Type	Namespace	Example
Array	System	int[] nums = {1,2,3};
List	System.Collections.Generic	List<int> list = new List<int>();
Dictionary	System.Collections.Generic	Dictionary<int,string> dict = new();
Queue	FIFO	Queue<string> q = new();
Stack	LIFO	Stack<int> s = new();

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LINQ (Language Integrated Query)

LINQ simplifies querying data in collections.

int[] numbers = { 1, 2, 3, 4, 5 };
var even = from n in numbers where n % 2 == 0 select n;

foreach(var n in even)
    Console.WriteLine(n);

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File Handling in C#

using System.IO;

File.WriteAllText("file.txt", "Hello C#");
string content = File.ReadAllText("file.txt");
Console.WriteLine(content);

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Exception Handling in C#

try {
    int x = 0;
    int y = 10 / x;
}
catch (DivideByZeroException e) {
    Console.WriteLine(e.Message);
}
finally {
    Console.WriteLine("Cleanup code");
}

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Asynchronous Programming in C#

async Task FetchData() {
    await Task.Delay(1000);
    Console.WriteLine("Data loaded");
}

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C# Keywords Summary Table

Keyword	Purpose
public	Accessible from anywhere
private	Accessible only within class
protected	Accessible in derived class
static	Belongs to class, not instance
const	Constant value
readonly	Assigned only once
virtual	Overridable method
override	Replaces base method
abstract	Must be implemented in child class
interface	Defines contract
using	Imports namespaces or disposes resources

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FAQ — C# Programming

Q1: Is C# only used for Windows applications?
No, modern .NET Core allows C# apps to run on Windows, Linux, and macOS.

Q2: What is the difference between C++ and C#?
C++ is a compiled system-level language, while C# runs on the .NET runtime and is designed for managed, high-level development.

Q3: Can I use C# for game development?
Yes, Unity Engine uses C# for all its game scripts.

Q4: Is C# easy to learn for beginners?
Yes! Its syntax is clean, modern, and similar to C, Java, and JavaScript.

Q5: Where can I practice C# online?
Try the PHPOnline C# Compiler for running C# code instantly.

# Summary

Here is what you've learned in this lesson:

• C# Cheat Sheet — Quick Reference Guide for Developers
• C# Basics for Beginners
• Data Types in C#
• C# Variables and Constants
• Operators in C#
• Conditional Statements in C#
• Loops in C#
• C# Functions (Methods)
• C# Object-Oriented Programming (OOP)
• C# Collections
• LINQ (Language Integrated Query)
• File Handling in C#
• Exception Handling in C#
• Asynchronous Programming in C#
• C# Keywords Summary Table
• FAQ — C# Programming