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New feature Optional Argument in C# 4.0

Posted By:Dhananjay Kumar       Posted Date: December 08, 2009    Points: 25    Category: C#    URL: http://www.dotnetspark.com  

New feature Optional Argument in C# 4.0.


This article will give a very basic introduction of Optional Argument in C#4.0. This article will explain how Operation overloading and Optional Argument is different with samples. This article will give different syntax with Named parameter to work with Optional arguments.

Optional Argument:


Five facts about Optional Parameter:

  1. Each Optional Parameter has a default value as its part of the definition.
  2. If no argument is sent for the Optional Parameter default is being used.
  3. Default value of the Optional Parameter must be constant
  4. Optional Parameter must define at the end of the any required parameter.
  5. Optional Parameter could be applied on Constructor, Method, and Indexer etc.

Syntax of Optional Arguments


Above is a Display function. This function is having two Required Parameters and two Optional Parameters. Optional Parameters are having their constant default value assigned at definition itself.

Intellisense indicates values for Optional Parameters.



Optional Argument and Operation overloading

We may say , Optional Argument is smart way to achieve Operation overloading. In Operation Overloading, we had more than one defintion for one operation. Each operation is having their own parameter list. Caller is calling the required operation by passing the matched parameter list. Where as in Optional Argument , there is only one definition of Function . Only one definition contains all the required and optional arguemnts.


My Function name is Display. This function is having required and Optional arguments. This function is just printing the values passed to it.

static void Display(string Name, int Age, string Sex = "Male", string Location = "India")
  Console.WriteLine("{0}\n{1}\n{2}\n{3}", Name, Age, Sex, Location);

Calling way 1:

I am passing all the values explicitly, while calling the Display function.

Display("Dhananjay Kumar", 25, "M", "Jamshedpur");



Calling way 2:

I am passing only required values. Default values for Optional Argument will get printed.

Display(Name: "Dhananjay Kumar", Age: 25);



Calling way 3:

I am passing value for Sex but omitting value for Location. This could only be done using Named Parameter.

Display("Dhananjay Kumar",25,Location:"Kerala");

If we will try like below,

Display("Dhananjay Kumar",,"Jamshedpur");

We will get compile time error as, Argument Missing.


So, we could have Optional Parameter at last else , we need to use Named parameter to call the function.

For your reference the entire code is as below,


using System;
System.Text;  namespace OptionalParmeterSample
  class Program
  static void Main(string[] args)
  Display(Name: "Dhananjay Kumar", Age: 25);
  Display("Dhananjay Kumar", 25, "M", "Jamshedpur");
  Display("Dhananjay Kumar",25,Location:"Kerala");
  // Display("Dhananjay Kumar",,"Jamshedpur");
  static void Display(string Name, int Age, string Sex = "Male", string Location = "India")
  Console.WriteLine("{0}\n{1}\n{2}\n{3}", Name, Age, Sex, Location);




In this article, I talked about Optional Parameter feature of c#4.0. Please download attached source code for better reference. Thanks for reading.

Happy Coding

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