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C# Cheat Sheet

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

Programming
Object-Oriented
Class

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.

C Strings

Member Example

// Using property of System.String
string lengthOfString = "How long?";
lengthOfString.Length           // => 9
// Using methods of System.String
lengthOfString.Contains("How"); // => true

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.";

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.

String interpolation

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

String concatenation

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

Getting Started

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);
}

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};

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");
}

User Input

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

Strings

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

See: Strings

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 \*\*/

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

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 = "quickref.me";
var num = 999;
var str = "999";
var bo = false;

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!