using System;

public class Program

{

    public static void Main(string[] args)

    {

        int[] a = { 1, 2, 3, 4 };

        int[] b = { 3, 4, 5, 6, 7, 8 };

        int[] c = GetDifference(a, b);

        foreach(var cx in c)

        {

            Console.Write(cx + ", ");   

        }

        Console.WriteLine();

        int[] d = GetCompliment(a, b);

        foreach(var dx in d)

        {

            Console.Write(dx + ", ");   

        }

    }

    // Get an array of all elements in b that are not in a

    // This is identical to calling GetDifference with the inputs reversed so lets just do that

    static int[] GetCompliment(int[] a, int[] b) { return GetDifference(b, a); }

​

    // Get an array of all elements in a that are not in b

    static int[] GetDifference(int[] a, int[] b) 

    {

        // Create the buffer array at the worst-case length which is the length

        // of a (where none of the elements in a are in b)

        int[] c = new int[a.Length];

​

        // Track how many elements we are actually ending up with

        int length = 0;

​

        // Loop through every element in a

        foreach (var ax in a)

        {

            bool found = false;

            // Loop through every element in b to see if it exists in a

            foreach (var bx in b)

            {

                if (ax == bx)

                {

                    // If the element was found in b, there's no reason to keep looping

                    found = true;

                    break;

                }

            }

​

            // Only save the element if it was not found in b

            if (!found)

            {

                c[length] = ax;

                length++;

            }

        }

​

        // Create the result array using the length of actual elements found

        int[] result = new int[length];

​

        // Copy the relevant slice of the buffer array into the result array

        Array.Copy(c, result, length);

​

        // Return the result array

        return result;

    }

}