Parameter arrays

Parameter arrays allow a variable number of arguments to be passed into a function member. The definition of the parameter has to include the params modifier, but the use of the parameter has no such keyword. A parameter array has to come at the end of the list of parameters, and must be a single-dimensional array. When using the function member, any number of parameters (including none) may appear in the invocation, so long as the parameters are each compatible with the type of the parameter array. Alternatively, a single array may be passed, in which case the parameter acts just as a normal value parameter.

For example:

void ShowNumbers (params int[] numbers)
{
    foreach (int x in numbers)
    {
        Console.Write (x+" ");
    }
    Console.WriteLine();

}

...

int[] x = {1, 2, 3};
ShowNumbers (x);
ShowNumbers (4, 5);

EXAMPLE

using System;
using System.Text;

public class Example9
{
    // Note that ShowNumbers is declared static here just
    // to make the sample app simple, so we don't
    // need to instantiate the example class. This
    // has no bearing on the parameter passing
    // discussed
    static void ShowNumbers (params int[] numbers)
    {
        foreach (int x in numbers)
        {
            Console.Write (x+" ");
        }
        Console.WriteLine();
    }

    public static void Main (string[] args)
    {
        int[] x = {1, 2, 3};
        ShowNumbers (x);
        ShowNumbers (4, 5);
    }

}

 Output:
1 2 3
4 5

In the first invocation, the variable x is passed by value, as it's just an array. In the second invocation, a new array of ints is created containing the two values specified, and a reference to this array is passed.

Mini-glossary

Some informal definitions and summaries of terms:

Function member :
         A function member is a method, property, event, indexer, user-defined operator, instance constructor, static constructor, or
destructor.

Output parameter
        A parameter very similar to a reference parameter, but with different definite assignment rules.

Reference parameter (pass-by-reference semantics)
       A parameter which shares the storage location of the variable used in the function member invocation. As they share the same storage location, they always have the same value (so changing the parameter value changes the invocation variable value).

Reference type
       Type where the value of a variable/expression of that type is a reference to an object rather than the object itself.

Storage location
        A portion of memory holding the value of a variable.

Value parameter (the default semantics, which are pass-by-value)
        A value parameter that has its own storage location, and thus its own value. The initial value is the value of the expression used in the function member invocation.

Value type
        Type where the value of a variable/expression of that type is the object data itself.