Copying Arrays

Part of the Fundamentals section of Coddy's C# journey. Lesson 58 of 70.

To copy elements from one array into another, use Array.Copy. It takes five arguments:

Array.Copy(source, sourceIndex, destination, destinationIndex, length);

It takes length elements from source, starting at sourceIndex, and writes them into destination, starting at destinationIndex. The destination array must already exist and be big enough.

The last argument is a count: how many elements to copy, not where to stop.

int[] scores = {90, 75, 60, 85};
int[] firstTwo = new int[2];
Array.Copy(scores, 0, firstTwo, 0, 2);
// firstTwo will be {90, 75}

destinationIndex is where the first copied element lands. Using source.Length as the count copies the whole array, whatever its size:

int[] source = {1, 2, 3};
int[] destination = new int[6];
Array.Copy(source, 0, destination, 3, source.Length);
// destination will be {0, 0, 0, 1, 2, 3}

To put one array after another, copy the second one to the position where the first one ends. That position is the first array's Length:

int[] first = {1, 2};
int[] second = {7, 8, 9};
int[] all = new int[first.Length + second.Length];
Array.Copy(first, 0, all, 0, first.Length);
Array.Copy(second, 0, all, first.Length, second.Length);
// all will be {1, 2, 7, 8, 9}

When both arrays start at index 0, there is a shorter form, Array.Copy(source, destination, length):

int[] source = {4, 5, 6, 7};
int[] destination = new int[3];
Array.Copy(source, destination, 3);
// destination will be {4, 5, 6}

Challenge

Easy

Create a method named AddToEnd that receives an array of strings and a string item. It returns a new array that holds every element of the array, in the same order, with item added at the end.

For example, AddToEnd(new string[] {"a", "b", "c"}, "d") returns ["a", "b", "c", "d"].

Use Array.Copy() to copy the elements into the new array.

Input format (2 lines):

Line 1: the array elements separated by commas (e.g. a,b,c)
Line 2: the item to add (e.g. d)

Output format: the new array's elements separated by a comma and a space (e.g. a, b, c, d)

Try it yourself

using System;

public class Program {
    public static string[] AddToEnd(string[] arr, string item) {
        // Write code here
    }

    public static void Main(string[] args) {
        string[] arr = Console.ReadLine().Split(',');
        string item = Console.ReadLine();
        string[] result = AddToEnd(arr, item);
        Console.WriteLine(string.Join(", ", result));
    }
}