In most C# interviews, the interviewer asks about a real-time example of extension method. So, here we will have a real time example of extension method for long data types, step by step.
This article demonstrates how to create extension method for long data types in C#. A few month ago I came across one of the requirements where I needed to display long data type numbers in a shortened format due to space constraints in the page. The number should be displayed in the page as below with a shortened fomat with suffix k, B and M (K indicates thousands, M - millions and B - Billions). Then I decided to create an extension method for long type and I am going to explain that here.
Requierment is to display numbers as below with suffix K,M,B.
  • 999 then 999
  • 1000 then 1k
  • 12000 then 12k
  • 110000 then 110K
  • 1120000 then 1.12M
  • 12300000 then 12.3M
  • 123400000 then 123.4M
  • 1234500000 then 1.235B and so on
Extension method allows you to add a new method to any existing type/class which were not part of the class. Extension method will help developer to extend the functionality of existing type without creating a new derived type, without changing existing type or without modifying existing type/orignal type.
Here I will explain how to create extension method for int type in C# step by step. A few points to remember while creating extension methods,
  • Class shoud be marked as static.
  • Method should be marked as static.
  • First parameter of extension method must be a type which you want to extend. In parameter this keyword is used to bind with what you want to extend.
Step 1
Let's start with window console application.
Real-Time Example Of Extension Method In C#
Step 2
Go to Add and click on New project then give project Name as ExtensionMethod and click on ok.
Real-Time Example Of Extension Method In C#
Step 3
Click on add new items and add new class.
Step 4
Write Extension method for long type.
  1. public static class LongExtension
  2. {
  3. public static string FormatNumberKMB(this long num)
  4. {
  5. if (num >= 100000000000)
  6. {
  7. return (num / 1000000000).ToString("0.#B");
  8. }
  9. if (num >= 1000000000)
  10. {
  11. return (num / 1000000000).ToString("0.##B");
  12. }
  13. if (num >= 100000000)
  14. {
  15. return (num / 1000000).ToString("0.#M");
  16. }
  17. if (num >= 1000000)
  18. {
  19. return (num / 1000000).ToString("0.##M");
  20. }
  21. if (num >= 100000)
  22. {
  23. return (num / 1000).ToString("0.#k");
  24. }
  25. if (num >= 10000)
  26. {
  27. return (num / 1000).ToString("0.##k");
  28. }
  29. if (num >= 1000)
  30. {
  31. return (num / 1000).ToString("0.#k");
  32. }
  34. return num.ToString("#,0");
  35. }
  36. }
Step 5
After adding extension method put logic with static method inside static class. As in the below image all long type numbers are applicable to use the above-created extension method. Once applied to any long type then this method will be able to be used on long type.
Real-Time Example Of Extension Method In C#
Step 6
How to use long extension method in application.
  1. class Program
  2. {
  3. static void Main(string[] args)
  4. {
  5. long number = 999;
  7. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  8. Console.WriteLine("-----------------------------------");
  10. number = 1000;
  11. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  12. Console.WriteLine("-----------------------------------");
  14. number = 12000;
  15. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  16. Console.WriteLine("-----------------------------------");
  18. number = 110000;
  19. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  20. Console.WriteLine("-----------------------------------");
  22. number = 1120000;
  23. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  24. Console.WriteLine("-----------------------------------");
  26. number = 12300000;
  27. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  28. Console.WriteLine("-----------------------------------");
  30. number = 123400000;
  31. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  32. Console.WriteLine("-----------------------------------");
  34. number = 1234560000;
  35. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  36. Console.WriteLine("-----------------------------------");
  38. number = 12345670000;
  39. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  40. Console.WriteLine("-----------------------------------");
  42. number = 123456780000;
  43. Console.WriteLine(number.ToString() + " Shorten To " + number.FormatNumberKMB());
  44. Console.WriteLine("-----------------------------------");
  46. Console.ReadLine();
  47. }
  48. }
Step 7
Let's have a look at the final result for the above scenarios.
Real-Time Example Of Extension Method In C#

Conclusion

Extension method allows you to add a new method without creating a new derived type, and without changing existing type. Here I have created long data types. In the same way you can create other types like int, decimal, string etc. I hope this article will help you to understand extension method with real time examples.