C#: From Fundamentals to Advanced Techniques?—?A Comprehensive Cheat Sheet
Sukhpinder Singh
.Net Technical Lead @ SourceFuse | .Net Modernization | Master's Degree in Software Systems
The comprehensive C# Cheat Sheet is designed to aid developers in mastering key syntax and concepts related to C# programming.
Contents
1. Basic Structure
All C# programs follow a fundamental structure, outlined below:
Starting with?.NET 5, top-level statements simplify the Program.cs content:
Console.WriteLine("Hello, World");
2. Data?Types
C# supports various data types such as:
3. Variables
Variables are symbolic names for values:
int age = 30; // integer variable
string name = "John"; // string variable
double PI = 3.14159; // double for floating-point numbers
bool isLoggedIn = true; // boolean variable
Use ‘var’ for type inference:
var number = 5; // compiler infers type as int
var message = "This is a message"; // compiler infers type as string
4. Constants
Constants hold immutable values:
const double GRAVITY = 9.81; // constant for gravitational acceleration
const string COMPANY_NAME = "MyCompany"; // constant company name
5. Conditional Statements
Control program flow based on conditions:
int age = 20;
if (age >= 18)
{
Console.WriteLine("You are eligible to vote.");
}
else
{
Console.WriteLine("You are not eligible to vote.");
}
switch (variable) { /*...*/ } // Switch statement
6. Loops
Execute code repeatedly:
for (int i = 1; i <= 5; i++)
{
Console.WriteLine(i);
}
foreach (var item in collection) { /*...*/ } // Foreach loop
while (condition) { /*...*/ } // While loop
do { /*...*/ } while (condition); // Do-while loop
7. Arrays
Fixed-size collections of elements:
string[] names = new string[3] { "Alice", "Bob", "Charlie" };
Console.WriteLine(names[1]); // Output: Bob (accessing element at index 1)
8. Lists
Dynamic collections similar to arrays:
List<int> numbers = new List<int>();
numbers.Add(1);
numbers.Add(2);
numbers.Add(3);
foreach (var number in numbers)
{
Console.WriteLine(number);
}
9. Dictionaries
Key-value pairs for data association:
Dictionary<string, string> phonebook = new Dictionary<string, string>();
phonebook.Add("John Doe", "123-456-7890");
phonebook.Add("Jane Doe", "987-654-3210");
Console.WriteLine(phonebook["John Doe"]); // Output: 123-456-7890
10. Methods
Encapsulate reusable logic:
public class Rectangle
{
public double Width { get; set; }
public double Height { get; set; }
public double GetArea()
{
return Width * Height;
}
}
public class Program
{
public static void Main(string[] args)
{
Rectangle rect = new Rectangle();
rect.Width = 5;
rect.Height = 10;
double area = rect.GetArea();
Console.WriteLine($"Area of rectangle: {area}");
}
}
11. Classes &?Objects
Classes define blueprints for objects:
public class MyClass // Class definition
{
public string PropertyName { get; set; } // Properties store data
public void MethodName() { /*...*/ } // Methods define actions
}
MyClass obj = new MyClass(); // Object creation
12. Exception Handling
Manage runtime errors gracefully:
public static int GetNumberInput()
{
while (true)
{
try
{
Console.WriteLine("Enter a number: ");
string input = Console.ReadLine();
return int.Parse(input);
}
catch (FormatException)
{
Console.WriteLine("Invalid input. Please enter a number.");
}
}
}
public static void Main(string[] args)
{
int number = GetNumberInput();
Console.WriteLine($"You entered: {number}");
}
13. Delegates, Events &?Lambda
For event-driven programming and method handling:
public delegate void MyDelegate(); // Delegate declaration
event MyDelegate MyEvent; // Event declaration
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void Main(string[] args)
{
List<Person> people = new List<Person>()
{
new Person { Name = "Alice", Age = 30 },
new Person { Name = "Bob", Age = 25 },
new Person { Name = "Charlie", Age = 40 },
};
people.Sort((p1, p2) => p1.Name.CompareTo(p2.Name));
foreach (var person in people)
{
Console.WriteLine(person.Name); // Output: Alice, Bob, Charlie (sorted by name)
}
}
14. LINQ (Language-Integrated Query)
Query capabilities for data manipulation:
using System.Linq;
public static void Main(string[] args)
{
List<int> numbers = new List<int>() { 1, 2, 3, 4, 5, 6 };
var evenNumbers = numbers.Where(x => x % 2 == 0);
foreach (var number in evenNumbers)
{
Console.WriteLine(number); // Output: 2, 4, 6
}
}
15. Attributes
Add metadata to code elements:
[Obsolete("Use the new DoSomethingV2 method instead.")]
public void DoSomething()
{
// Implementation here
}
public void DoSomethingV2()
{
// New and improved implementation
}
16. Async/Await
For non-blocking code execution:
using System.Threading.Tasks;
public static async Task DownloadFileAsync(string url, string filePath)
{
// Simulate downloading data asynchronously
await Task.Delay(2000); // Simulate a 2-second download
// Write downloaded data to the file
File.WriteAllText(filePath, "Downloaded content");
Console.WriteLine($"File downloaded to: {filePath}");
}
public static void Main(string[] args)
{
string url = "https://example.com/data.txt";
string filePath = "downloaded_data.txt";
DownloadFileAsync(url, filePath);
// Continue program execution while download happens in the background
Console.WriteLine("Downloading file...");
Console.WriteLine("Meanwhile, you can do other things...");
}
17. Miscellaneous
Additional language features:
18. String Manipulation
Powerful string handling methods:
string.Concat(); // Combine strings
string.Join(); // Join elements
str.Split(); // Split string
str.ToUpper(); // Convert to uppercase
str.ToLower(); // Convert to lowercase
19. File?I/O
Operations with files:
using System.IO; // Required for File I/O
File.ReadAllText(path); // Read file content
File.WriteAllText(path, content); // Write to file
File.Exists(path); // Check file existence
20. Date &?Time
Date and time manipulation:
领英推荐
using System;
public static void Main(string[] args)
{
DateTime startDate = DateTime.Parse("2024-03-10");
DateTime endDate = DateTime.Now;
TimeSpan difference = endDate - startDate;
Console.WriteLine($"Time difference: {difference.Days} days, {difference.Hours} hours");
}
21. Generics
Type-safe data structures:
public class Stack<T>
{
private List<T> items = new List<T>();
public void Push(T item)
{
items.Add(item);
}
public T Pop()
{
T item = items[items.Count - 1];
items.RemoveAt(items.Count - 1);
return item;
}
}
public static void Main(string[] args)
{
Stack<string> messages = new Stack<string>();
messages.Push("Hello");
messages.Push("World");
string message = messages.Pop();
Console.WriteLine(message); // Output: World
}
22. Nullables
Allow value types to be null:
int? nullableInt = null; // Nullable integer
23. Attributes & Reflection
Metadata and type introspection:
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void Main(string[] args)
{
Type personType = typeof(Person);
PropertyInfo[] properties = personType.GetProperties();
foreach (PropertyInfo property in properties)
{
Console.WriteLine(property.Name); // Output: Name, Age
}
}
24. Extension Methods
Add methods to existing types:
public static class StringExtensions
{
public static string ToUppercase(this string str)
{
return str.ToUpper();
}
}
public static void Main(string[] args)
{
string message = "Hello, world!";
string uppercased = message.ToUppercase(); // Using the extension method
Console.WriteLine(uppercased); // Output: HELLO, WORLD!
}
25. Dependency Injection
Loosely coupled code design:
public interface ILogger
{
void LogMessage(string message);
}
public class MyService
{
private readonly ILogger _logger;
public MyService(ILogger logger)
{
_logger = logger;
}
public void DoSomething()
{
_logger.LogMessage("Doing something...");
}
}
// Implementing the ILogger interface (example)
public class ConsoleLogger : ILogger
{
public void LogMessage(string message)
{
Console.WriteLine(message);
}
}
public static void Main(string[] args)
{
ILogger logger = new ConsoleLogger();
MyService service = new MyService(logger);
service.DoSomething();
}
26. Partial?Classes
Splitting a single class definition:
public partial class MyClass { /*...*/ } // Partial class definition
27. Interoperability
Interop with other languages:
using System;
using System.Runtime.InteropServices;
[DllImport("user32.dll")]
public static extern int MessageBox(IntPtr hWnd, string lpText, string lpCaption, uint uType);
public static void Main(string[] args)
{
MessageBox(IntPtr.Zero, "Hello from C#!", "Interop Example", 0);
}
28. Anonymous Types
Creating unnamed types:csharpCopy code
var person = new { Name = "John", Age = 30 };
Console.WriteLine($"Name: {person.Name}, Age: {person.Age}");
29. Tuple
Data structures with a specific number of elements:
(string Name, int Age) person = ("Alice", 30);
Console.WriteLine($"Name: {person.Name}, Age: {person.Age}"); // Accessing elements using Item1 and Item2
30. Pattern?Matching
Simplifies certain programming tasks:
object obj = new Person { Name = "Bob", Age = 25 };
if (obj is Person { Name: "Bob", Age >= 18 })
{
Console.WriteLine("Bob is an adult.");
}
31. Local Functions
Encapsulate logic within methods:
public static int Calculate(int number)
{
int Factorial(int n)
{
if (n == 0) return 1;
return n * Factorial(n - 1);
}
return Factorial(number);
}
public static void Main(string[] args)
{
int result = Calculate(5);
Console.WriteLine($"5! = {result}");
}
32. Records
Concise syntax for reference types:
public record Person(string Name, int Age);
public static void Main(string[] args)
{
Person person1 = new Person("Alice", 30);
Person person2 = new Person("Alice", 30);
// Records provide default equality comparison
if (person1 == person2)
{
Console.WriteLine("People are equal");
}
}
33. with Expressions
Non-destructive mutation for records:
var john = new Person("John", 30);
var jane = john with { Name = "Jane" }; // Non-destructive mutation
34. Indexers and?Ranges
Flexible data access:
int[] arr = {0, 1, 2, 3, 4, 5};
var subset = arr[1..^1]; // Indexer and range usage
35. using Declaration
Dispose of IDisposable objects:
using var reader = new StreamReader("file.txt"); // using declaration
36. Nullable Reference Types?(NRTs)
Avoid null reference exceptions:
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void Main(string[] args)
{
Person person = new Person() { Age = 30 };
// NRTs require null checks before accessing properties
if (person?.Name != null)
{
Console.WriteLine(person.Name);
}
else
{
Console.WriteLine("Name is null");
}
}
37. Pattern-Based Using
More patterns in the using statement:
public ref struct ResourceWrapper { /*...*/ } // Resource wrapper
using var resource = new ResourceWrapper(); // Pattern-based using
38. Property?Patterns
Deconstruct objects in pattern matching:
if (obj is Person { Name: "John", Age: var age }) { /*...*/ } // Property pattern matching
39. Default Interface Implementations
Interfaces with default method implementations:
public interface IPerson { /*...*/ } // Interface with default method
public class MyClass : IPerson { /*...*/ } // Class implementing interface
40. Dynamic?Binding
Runtime type resolution:
dynamic d = 5; // Dynamic binding
d = "Hello"; // No compile-time type checking
Conclusion
This structured C# Cheat Sheet concludes with advanced topics and techniques, providing a comprehensive reference for developers aiming to enhance their C# programming skills. For detailed examples and further exploration, refer to the specific sections outlined in this guide. Happy coding!
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