C# 3.0 Cookbook, 3rd Edition

5.1. Swapping Two Elements in an Array

Problem

You want an efficient method to swap two elements that exist within a single array.

Solution

Use the generic SwapElementsInArray<T> method that extends the generic Array type:

	public static void SwapElementsInArray<T>(this T[] theArray, int index1, int
index2)
	{
	    T tempHolder = theArray[index1];
	    theArray[index1] = theArray[index2];
	    theArray[index2] = tempHolder;
	    }

Discussion

There is no specific method in the .NET Framework that allows you to swap only two specific elements within an array. The SwapElementsInArray method presented in this recipe allows for only two specified elements of an array (specified in the index1 and index2 arguments to this method).

The following code uses the SwapElementsInArray<T> method to swap the zeroth and fourth elements in an array of integers:

	public static void TestSwapArrayElements()
	{
	    int[] someArray = {1,2,3,4,5};

	    for (int counter = 0; counter < someArray.Length; counter++)
	    {
	        Console.WriteLine("Element " + counter + " = " + someArray[counter]);
	    }

	    someArray.SwapElementsInArray(0, 4);

	    for (int counter = 0; counter < someArray.Length; counter++)
	    {
	        Console.WriteLine("Element " + counter + " = " + someArray[counter]);
	    }
	}

This code produces the following output:

	Element 0 = 1 ← The original array
	Element 1 = 2
	Element 2 = 3
	Element 3 = 4
	Element 4 = 5

	Element 0 = 5 ← The array with elements swapped
	Element 1 = 2
	Element 2 = 3
	Element 3 = 4
	Element 4 = 1