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params (C# Reference)

The params keyword lets you specify a method parameter that takes a variable number of arguments.

You can send a comma-separated list of arguments of the type specified in the parameter declaration, or an array of arguments of the specified type. You also can send no arguments.

No additional parameters are permitted after the params keyword in a method declaration, and only one params keyword is permitted in a method declaration.

The following example demonstrates various ways in which arguments can be sent to a params parameter.


public class MyClass
{
    public static void UseParams(params int[] list)
    {
        for (int i = 0; i < list.Length; i++)
        {
            Console.Write(list[i] + " ");
        }
        Console.WriteLine();
    }

    public static void UseParams2(params object[] list)
    {
        for (int i = 0; i < list.Length; i++)
        {
            Console.Write(list[i] + " ");
        }
        Console.WriteLine();
    }

    static void Main()
    {
        // You can send a comma-separated list of arguments of the 
        // specified type.
        UseParams(1, 2, 3, 4);
        UseParams2(1, 'a', "test");

        // A params parameter accepts zero or more arguments.
        // The following calling statement displays only a blank line.
        UseParams2();

        // An array argument can be passed, as long as the array
        // type matches the parameter type of the method being called.
        int[] myIntArray = { 5, 6, 7, 8, 9 };
        UseParams(myIntArray);

        object[] myObjArray = { 2, 'b', "test", "again" };
        UseParams2(myObjArray);

        // The following call causes a compiler error because the object
        // array cannot be converted into an integer array.
        //UseParams(myObjArray);

        // The following call does not cause an error, but the entire 
        // integer array becomes the first element of the params array.
        UseParams2(myIntArray);
    }
}
/*
Output:
    1 2 3 4
    1 a test

    5 6 7 8 9
    2 b test again
    System.Int32[]
*/


For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

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