AddNumbers

using System;
using System.Collections.Generic;


class Program
{
    //Write a method that adds two positive integer numbers represented as arrays of digits
    //(each array element arr[i] contains a digit; the last digit is kept in arr[0]).
    //Each of the numbers that will be added could have up to 10 000 digits.

    static void Main()
    {
        int[] number1 = {7,8,4,2,6};
        int[] number2 = {1,2,3,4,4,5,8,9};
        AddNumbers(number1, number2);
    }
    static void AddNumbers (int[]number1, int[]number2)
    {
        int add = 0;
        int resultLength=Math.Max(number1.Length, number2.Length) + 1;
        int[] result = new int[resultLength];

        for (int i = 0; i < resultLength-1; i++)
        {
            if (i < Math.Min(number1.Length, number2.Length))
            {
                if ((number1[i] + number2[i]) < 10)
                {
                    result[result.Length - i - 1] = number1[i] + number2[i] + add;
                    add = (number1[i] + number2[i] + add) / 10;
                }
                else if ((number1[i] + number2[i]) >= 10)
                {
                    result[result.Length - i - 1] = (number1[i] + number2[i] + add) % 10;
                    add =(number1[i] + number2[i] + add)/ 10;
                }
            }
            else if(i>= Math.Min(number1.Length, number2.Length))
            {
                if ((Math.Max(number1.Length, number2.Length) == number1.Length))
                {

                    if ((number1[i] + add) < 10)
                    {
                        result[result.Length - i - 1] = number1[i] + add;
                        add = (number1[i] + add) / 10;
                    }
                    else if ((number1[i] + add) >= 10)
                    {
                        result[result.Length - i - 1] = (number1[i] + add) % 10;
                        add = (number1[i] + add) / 10;
                    }
                }
                else if ((Math.Max(number1.Length, number2.Length) == number2.Length))
                {
                    if ((number2[i] + add) < 10)
                    {
                        result[result.Length - i - 1] = number2[i] + add;
                        add = (number2[i] + add) / 10;
                    }
                    else if ((number2[i] + add) >= 10)
                    {
                        result[result.Length - i - 1] = (number2[i] + add) % 10;
                        add = (number2[i] + add) / 10;
                    }
                }
            }

        }

        // Print the result
        for (int i = 0; i < number1.Length; i++)
        {
            Console.Write(number1[i]);
        }
        Console.WriteLine();
        Console.WriteLine("+");

        for (int i = 0; i < number2.Length; i++)
        {
            Console.Write(number2[i]);
        }
        Console.WriteLine();
        Console.WriteLine(new string('-',resultLength));

        if (result[0] == 0)
        {
            for (int i = 1; i < result.Length; i++)
            {
                Console.Write(result[i]);
            }
        }
        else
        {
            for (int i = 0; i < result.Length; i++)
            {
                Console.Write(result[i]);
            }
        }
        Console.WriteLine();
    }
}