freeCodeCamp/guide/english/csharp/switch-case/index.md

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Switch Case

Switch Case

Switch is a selection statement that chooses a switch case section depending on the value matched with the expression/value being evaluated.¹ If none of the case statements match the value of the switched variable, the default path is chosen. The switch statement is like a set of if statements. We exit from the switch by break.

Example

public enum Colors { Red, Blue, Green, Orange }

Colors myColor;

... myColor is set to one of the enum values ...

switch(myColor){
  case Colors.Red: 
    Console.WriteLine("How you like them apples?");
    break;
  case Colors.Blue: 
    Console.WriteLine("Ice Ice Baby...");
    break;
  case Colors.Green: 
    Console.WriteLine("Fore!");
    break;
  default:
    Console.WriteLine("I have a hard time when I try to rhyme.");
}

Output

If myColor is Colors.Red:
> How you like them apples?

If myColor is Colors.Blue:
> Ice Ice Baby...

If myColor is Colors.Green:
> Fore!

If myColor is Colors.Orange:
> I have a hard time when I try to rhyme.

Fallthrough

It is also possible to use multiple statements produce the same outcome, by letting the cases 'fallthrough', like so:

switch(myColor) {
  case Colors.Red:
  case Colors.Blue:
    //Code
    break;
  ...
 }

This will execute the same lines of code if myColor is either Red or Blue.

When clause

Starting with C# 7.0 you can use when clause to specify additional condition that must be satisfied. When clause is optional and is used right after specific case.

Dog dog = new Dog
{
    Name = "Charlie",
    Breed = "Affenpinscher",
    Age = 3
};

switch (dog)
{
    case Dog d when d.Breed == "Affenpinscher" && d.Age >= 6:
        Console.WriteLine($"{dog.Name} is considered a senior dog.");
        break;
    case Dog d when d.Breed == "Affenpinscher" && d.Age >= 2:
        Console.WriteLine($"{dog.Name} is considered an adult dog.");
        break;
    case Dog d when d.Breed == "Affenpinscher":
        Console.WriteLine($"{dog.Name} is considered a puppy.");
        break;
    case Dog d when d.Breed == "Chihuahua" && d.Age >= 4:
        Console.WriteLine($"{dog.Name} is considered a senior dog.");
        break;
    case Dog d when d.Breed == "Chihuahua" && d.Age >= 2:
        Console.WriteLine($"{dog.Name} is considered an adult dog.");
        break;
    case Dog d when d.Breed == "Chihuahua":
        Console.WriteLine($"{dog.Name} is considered a puppy.");
        break;
    default:
        Console.WriteLine($"We have no information according {dog.Breed} breed.");
        break;
}

As you see in the above example after when keyword you should specify logical condition (an instruction that returns bool value).

Pattern matching using switch case

We can use switch to not only match certain values, but also match certain data type. This is called pattern matching

Example

Lets say that we have some different types of shapes:

  public class Square
  {
      public double Side { get; }

      public Square(double side)
      {
          Side = side;
      }
  }
  
  public class Circle
  {
      public double Radius { get; }

      public Circle(double radius)
      {
          Radius = radius;
      }
  }
  
  public struct Rectangle
  {
      public double Length { get; }
      public double Height { get; }

      public Rectangle(double length, double height)
      {
          Length = length;
          Height = height;
      }
  }

And now we want to create a method which calculates area for any shape we pass to it. We can do that using pattern matching in switch statement like so:

  public static double ComputeAreaModernSwitch(object shape)
  {
      switch (shape)
      {
          case Square s:
              return s.Side * s.Side;
          case Circle c:
              return c.Radius * c.Radius * Math.PI;
          case Rectangle r:
              return r.Height * r.Length;
          default:
              throw new ArgumentException(
                  message: "shape is not a recognized shape",
                  paramName: nameof(shape));
      }
  }

Sources:

• 1 https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/switch
• https://docs.microsoft.com/en-us/dotnet/csharp/pattern-matching