Non primitive type

Class

public class Person
{
  public string Name;

  public void Greet()
  {
    Console.WriteLine("Hi, my name is " + Name);
  }
}

Struct

Struct is similar to class. But, it's smaller and less powerful. It's useful for creating a commonly reused simple object. For example, a point has x and y.

public struct Point
{
  public int X;
  public int Y;
}

Array

In c#, array has a fixed size.

// init an array with ten 0
int[] nums = new int[10];

// init an array with the content.
int[] counts = new int[3] {1, 2, 3};

// get an element of an array by index
Console.WriteLine(nums[0]);

String

String is immutable. If you want to build a complex string, use StringBuilder class.

To join the string:

// option 1
const string name = firstName + " " + lastName;

// option 2
const string name = string.Format("{0} {1}", firstName, lastName);

// option 3
const string[] words = new string[2] {firstName, lastName};
const string name = string.Join(" ", words);

Enum

public enum PayMethod
{
  Cash = 0,
  Card = 1,
  Phone = 2
}

var method = PayMethod.Card

By default, the elements of enum is int. We can set it to byte.

public enum PayMethod : byte

// int to enum
const int methodId = 1;
var method = (PayMethod)methodId;

// enum to string
string methodName = method.ToString();

// string to enum
var method = (PayMethod)Enum.Parse(typeof(PayMethod), "Card");

Value type vs Reference type

Value type includes primitive and struct. It is allocated on the stack. Memory allocation is done automatically. It will be removed immediately when it's out of memory.

Reference type inclues non primitive. It is allocated on the heap. Memory allocation is done by manually new. The memory is released by garbage collection of CLR.