Can I give a default value to parameters or optional parameters in C# functions?

Question

Can I give default parameters in C#?

In C:

void fun(int i = 1)
{
    printf("%d", i);
}

Can we give parameters a default value? Is it possible in C#? If so, can we avoid overloading functions?

It's always a bad practice to add an optional parameter to an existing function. If you are working on a project which is having to refer the class having a function and we changed a parameter with an optional value, it may throw a run time exception that the method is not found.

This is because we will consider that the if we add an extra optional value, there is no code change required if the function is used in many places.

function Add(int a, int b);

This will be called using this way:

Add(10, 10);

But if we add an optional parameter like this,

function Add(int a, int b, int c = 0);

then the compiler expects

Add(10, 10, 0);

Actually we are calling like this Add(10, 10) and this function won't be available in that class and causes a run time exception.

This happens for while adding a new parameter to a function which called by a lot of places and I not sure this will happen every time. But I suggest you to overload the function.

Always we need to overload the method which has an optional parameter. Also if you are working with functions having more than one optional parameter, then it's good to pass the value using the name of the parameter.

function Add(int a, int b, int c = 0);

It's always good to call this function using the following way.

Add(10, 20, c:30);

possible duplicate of How can you use optional parameters in C#? — nawfal
– nawfal, Commented May 16, 2013 at 10:46
@nawfal it has asked a long back and while working with optional param I got some issues. So i updated the question. — kbvishnu
– kbvishnu, Commented May 18, 2013 at 13:31
@VeeKayBee thats right, but did you have some question there (in the edit)? If you want to make that point, why not answer it in a relevant thread (possibly even this)? — nawfal
– nawfal, Commented May 18, 2013 at 13:34

Chuck · Accepted Answer · 2010-10-12 12:52:35Z

92

That is exactly how you do it in C#, but the feature was first added in .NET 4.0

answered Oct 12, 2010 at 12:52

Chuck

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3 Comments

Marek Kwiendacz Over a year ago

It is possible to use it in .NET 3.5

dbardakov Over a year ago

Visual Studio 2010+ has msbuild with multitargeting feature (msdn.microsoft.com/en-us/library/vstudio/…). It can use Target packs for .NET 4.0 to build your optional params into bunch of overloaded methods.

EricG Over a year ago

what about inline methods (Func, Action, delegate)?

Donut · Accepted Answer · 2010-10-12 12:52:49Z

57

Yes. See Named and Optional Arguments. Note that the default value needs to be a constant, so this is OK:

public string Foo(string myParam = "default value") // constant, OK
{
}

but this is not:

public void Bar(string myParam = Foo()) // not a constant, not OK
{
}

answered Oct 12, 2010 at 12:52

Donut

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Comments

Frederik Gheysels · Accepted Answer · 2010-10-12 12:55:46Z

27

It is only possible as from C# 4.0

However, when you use a version of C#, prior to 4.0, you can work around this by using overloaded methods:

public void Func( int i, int j )
{
    Console.WriteLine (String.Format ("i = {0}, j = {1}", i, j));
}

public void Func( int i )
{
    Func (i, 4);
}

public void Func ()
{
    Func (5);
}

(Or, you can upgrade to C# 4.0 offcourse).

answered Oct 12, 2010 at 12:55

Frederik Gheysels

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Comments

ChrisF · Accepted Answer · 2014-07-24 20:36:14Z

6

Yes, but you'll need to be using .NET 3.5 and C# 4.0 to get this functionality.

This MSDN page has more information.

edited Jul 24, 2014 at 20:36

answered Oct 12, 2010 at 12:52

ChrisF

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Comments

Marek Kwiendacz · Accepted Answer · 2014-07-24 20:06:07Z

1

This functionality is available from C# 4.0 - it was introduced in Visual Studio 2010. And you can use it in project for .NET 3.5. So there is no need to upgrade old projects in .NET 3.5 to .NET 4.0.

You have to just use Visual Studio 2010, but remember that it should compile to default language version (set it in project Properties->Buid->Advanced...)

This MSDN page has more information about optional parameters in VS 2010.

edited Jul 24, 2014 at 20:06

answered Jul 24, 2014 at 19:52

Marek Kwiendacz

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Comments

Øyvind Bråthen · Accepted Answer · 2010-10-12 12:52:58Z

0

This is a feature of C# 4.0, but was not possible without using function overload prior to that version.

answered Oct 12, 2010 at 12:52

Øyvind Bråthen

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