Learn C#: Intro to Classes

Burger cheeseburger = new Burger();
// If a class is a recipe, then an object is a single meal made from that recipe.

House tudor = new House();
// If a class is a blueprint, then an object is a house made from that blueprint.

class Program {
  static void Main(string[] args) 
  {
    string greeting = "hello";

    // Console is a class 
    // and WriteLine is one of its members
    Console.WriteLine(greeting.Length); // Prints 5

    Forest f = new Forest("Amazon Rainforest");

    // access members using dot "." notation
    f.AnnounceForest(); 
    // Prints "This forest is known as the Amazon Rainforest!"
  }
}

class Forest
{
  public string name;
  public Forest(string name) 
  {
    this.name = name;
  }

  public AnnounceForest() 
  {
    Console.WriteLine($"This forest is known as the {name}!")
  }
}

// We can use the this keyword to refer to the current class's members hidden by similar names:
public NationalPark(int area, string state)
{
  this.area = area;
  this.state = state;
}

// The code below requires duplicate code, which can lead to extra work and errors when changes are needed:
public NationalPark(int area, string state)
{
  area = area;
  state = state;
}
public NationalPark(int area)
{
  area = area;
  state = "Unknown";
}

// When "this" is used as a method 
// it instructs one constructor to call another
// the following achieves the same as the preceding 2 constructors
public NationalPark(int area) : this(are, "Unknown")
{ }

public class Person
{
   public string firstName;
   public string lastName;
}

// In this example, firstName and lastName are fields of the Person class.

public class Freshman
{
  public string firstName;
}

public static void Main (string[] args)
{
  Freshman f = new Freshman();
  // name is null
  string name = f.firstName;
}

// In this example, no constructor is defined in Freshman, but a parameterless constructor is still available for use in Main(). All fields will be set to a default value according to their type and remain unchanged until updated manually.

// Takes two arguments
public Forest(int area, string country)
{ 
  this.area = area;
  this.country = country;
}

// Takes one argument
public Forest(int area)
{ 
  this.area = area;
  this.country = "Unknown";
}


// Typically, a constructor is used to set initial values and run any code needed to “set up” an instance.

// A constructor looks like a method, but it does not include a return type and it must have the same name as the enclosing type.