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C# Method Parameters


Parameters and Arguments

Information can be passed to methods as parameter. Parameters act as variables inside the method.

They are specified after the method name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma.

The following example has a method that takes a string called fname as parameter. When the method is called, we pass along a first name, which is used inside the method to print the full name:

Example

static void MyMethod(string fname) 
{
  Console.WriteLine(fname + " Refsnes");
}

static void Main(string[] args)
{
  MyMethod("Liam");
  MyMethod("Jenny");
  MyMethod("Anja");
}

// Liam Refsnes
// Jenny Refsnes
// Anja Refsnes

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When a parameter is passed to the method, it is called an argument. So, from the example above: fname is a parameter, while Liam, Jenny and Anja are arguments.


Default Parameter Value

You can also use a default parameter value, by using the equals sign (=). If we call the method without an argument, it uses the default value ("Norway"):

Example

static void MyMethod(string country = "Norway") 
{
  Console.WriteLine(country);
}

static void Main(string[] args)
{
  MyMethod("Sweden");
  MyMethod("India");
  MyMethod();
  MyMethod("USA");
}

// Sweden
// India
// Norway
// USA

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A parameter with a default value, is often known as an "optional parameter". From the example above, country is an optional parameter and "Norway" is the default value.


Multiple Parameters

You can have as many parameters as you like:

Example

static void MyMethod(string fname, int age) 
{
  Console.WriteLine(fname + " is " + age);
}

static void Main(string[] args)
{
  MyMethod("Liam", 5);
  MyMethod("Jenny", 8);
  MyMethod("Anja", 31);
}

// Liam is 5
// Jenny is 8
// Anja is 31

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Note that when you are working with multiple parameters, the method call must have the same number of arguments as there are parameters, and the arguments must be passed in the same order.


Return Values

The void keyword, used in the examples above, indicates that the method should not return a value. If you want the method to return a value, you can use a primitive data type (such as int or double) instead of void, and use the return keyword inside the method:

Example

static int MyMethod(int x) 
{
  return 5 + x;
}

static void Main(string[] args)
{
  Console.WriteLine(MyMethod(3));
}

// Outputs 8 (5 + 3)

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This example returns the sum of a method's two parameters:

Example

static int MyMethod(int x, int y) 
{
  return x + y;
}

static void Main(string[] args)
{
  Console.WriteLine(MyMethod(5, 3));
}

// Outputs 8 (5 + 3)

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You can also store the result in a variable (recommended, as it is easier to read and maintain):

Example

static int MyMethod(int x, int y) 
{
  return x + y;
}

static void Main(string[] args)
{
  int z = MyMethod(5, 3);
  Console.WriteLine(z);
}

// Outputs 8 (5 + 3)

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Named Arguments

It is also possible to send arguments with the key: value syntax.

That way, the order of the arguments does not matter:

Example

static void MyMethod(string child1, string child2, string child3) 
{
  Console.WriteLine("The youngest child is: " + child3);
}

static void Main(string[] args)
{
  MyMethod(child3: "John", child1: "Liam", child2: "Liam");
}

// The youngest child is: John

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Named arguments are especially useful when you have multiple parameters with default values, and you only want to specify one of them when you call it:

Example

static void MyMethod(string child1 = "Liam", string child2 = "Jenny", string child3 = "John")
{
  Console.WriteLine(child3);
}

static void Main(string[] args)
{
  MyMethod("child3");
}

// John

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