What are virtual functions in C#?

The virtual keyword is useful in modifying a method, property, indexer, or event. When you have a function defined in a class that you want to be implemented in an inherited class(es), you use virtual functions. The virtual functions could be implemented differently in different inherited class and the call to these functions will be decided at runtime.

The following is a virtual function

public virtual int area() { }

Here is an example showing how to work with virtual functions −

Example

using System;

namespace PolymorphismApplication {
   class Shape {
      protected int width, height;
   
      public Shape( int a = 0, int b = 0) {
         width = a;
         height = b;
      }

      public virtual int area() {
         Console.WriteLine("Parent class area :");
         return 0;
      }
   }

   class Rectangle: Shape {
      public Rectangle( int a = 0, int b = 0): base(a, b) {

      }

      public override int area () {
         Console.WriteLine("Rectangle class area ");
         return (width * height);
      }
   }

   class Triangle: Shape {
      public Triangle(int a = 0, int b = 0): base(a, b) {
   }

   public override int area() {
      Console.WriteLine("Triangle class area:");
      return (width * height / 2);
   }
}

class Caller {
   public void CallArea(Shape sh) {
      int a;
      a = sh.area();
      Console.WriteLine("Area: {0}", a);
   }
}

class Tester {
   static void Main(string[] args) {
      Caller c = new Caller();
      Rectangle r = new Rectangle(10, 7);
      Triangle t = new Triangle(10, 5);

      c.CallArea(r);
      c.CallArea(t);
      Console.ReadKey();
   }
   }
}