C# cheatsheet

C# quick reference cheat sheet that provides basic syntax and methods.

#Getting Started

#Hello.cs

class Hello {
  // main method
  static void Main(string[] args)
  {
    // Output: Hello, world!
    Console.WriteLine("Hello, world!");
  }
}

Compiling and running (make sure you are in the project directory)

$ dotnet run
Hello, world!

#Variables

int intNum = 9;
long longNum = 9999999;
float floatNum = 9.99F;
double doubleNum = 99.999;
decimal decimalNum = 99.9999M;
char letter = 'D';
bool @bool = true;
string site = "ref.toolkits.cn";

var num = 999;
var str = "999";
var bo = false;

#Primitive Data Types

Data Type	Size	Range
`int`	4 bytes	-2³¹ ^to 2³¹-1
`long`	8 bytes	-2⁶³ ^to 2⁶³-1
`float`	4 bytes	6 ^to 7 decimal digits
`double`	8 bytes	15 decimal digits
`decimal`	16 bytes	28 ^to 29 decimal digits
`char`	2 bytes	0 ^to 65535
`bool`	1 bit	true / false
`string`	2 bytes per char	N/A

#Comments

// Single-line comment

/* Multi-line 
   comment */

// TODO: Adds comment to a task list in Visual Studio

/// Single-line comment used for documentation

/** Multi-line comment 
    used for documentation **/

#Strings

string first = "John";
string last = "Doe";

// string concatenation
string name = first + " " + last;
Console.WriteLine(name); // => John Doe

See: Strings

#User Input

Console.WriteLine("Enter number:");
if(int.TryParse(Console.ReadLine(),out int input))
{
  // Input validated
  Console.WriteLine($"You entered {input}");
}

#Conditionals

int j = 10;

if (j == 10) {
  Console.WriteLine("I get printed");
} else if (j > 10) {
  Console.WriteLine("I don't");
} else {
  Console.WriteLine("I also don't");
}

#Arrays

char[] chars = new char[10];
chars[0] = 'a';
chars[1] = 'b';

string[] letters = {"A", "B", "C"};
int[] mylist = {100, 200};
bool[] answers = {true, false};

#Loops

int[] numbers = {1, 2, 3, 4, 5};

for(int i = 0; i < numbers.Length; i++) {
  Console.WriteLine(numbers[i]);
}

foreach(int num in numbers) {
  Console.WriteLine(num);
}

#C# Strings

#String concatenation

string first = "John";
string last = "Doe";

string name = first + " " + last;
Console.WriteLine(name); // => John Doe

#String interpolation

string first = "John";
string last = "Doe";

string name = $"{first} {last}";
Console.WriteLine(name); // => John Doe

#String Members

Member	Description
Length	A property that returns the length of the string.
Compare()	A static method that compares two strings.
Contains()	Determines if the string contains a specific substring.
Equals()	Determines if the two strings have the same character data.
Format()	Formats a string via the {0} notation and by using other primitives.
Trim()	Removes all instances of specific characters from trailing and leading characters. Defaults to removing leading and trailing spaces.
Split()	Removes the provided character and creates an array out of the remaining characters on either side.

#Verbatim strings

string longString = @"I can type any characters in here !#@$%^&*()__+ '' \n \t except double quotes and I will be taken literally. I even work with multiple lines.";

#Member Example

// Using property of System.String
string lengthOfString = "How long?";
lengthOfString.Length           // => 9

// Using methods of System.String
lengthOfString.Contains("How"); // => true

#Misc

#General .NET Terms

Term	Definition
Runtime	A collection of services that are required to execute a given compiled unit of code.
Common Language Runtime (CLR)	Primarily locates, loads, and managed .NET objects. The CLR also handles memory management, application hosting, coordination of threads, performaing security checks, and other low-level details.
Managed code	Code that compiles and runs on .NET runtime. C#/F#/VB are examples.
Unmanaged code	Code that compiles straight to machine code and cannot be directly hosted by the .NET runtime. Contains no free memory management, garbage collection, etc. DLLs created from C/C++ are examples.