Calculate n! [1 , 100]

//Write a program to calculate n! for each n in the range[1..100]. Hint: Implement first a method
//that multiplies a number represented as array of digits by given integer number.

namespace Methods10
{
    using System;
    using System.Text;
    using System.Numerics;

    class FactorielMethod
    {
        public static int[] NumberMultiplyer(int[] arr, int digit)
        {
            int len = arr.Length;
            int[] tempArr = new int[len];
            int[] tempArr2 = new int[len];

            // Console.WriteLine("resultArr " + string.Join("", arr));

            for (int i = 0; i < arr.Length - 1; i++) // {0, 2, 1}   0  2  1
            {

                if (arr[i] != 0)
                {

                    for (int k = 0; k < len; k++)
                    {
                        tempArr[k] = 0;
                    }

                    int current = digit * arr[i];

                    for (int j = i; j < i + 3 ; j++)
                    {
                        tempArr[j] = current % 10;
                        current = current / 10;
                    }
                    tempArr2 = addArraysOfDigits(tempArr, tempArr2);
                }
            }

            return tempArr2;
        }

        static int [] addArraysOfDigits(int[] arr1, int[] arr2)
        {
            int maxLen = arr1.Length > arr2.Length ? arr1.Length : arr2.Length;

            int[] tempArr = new int[maxLen + 1];
            int[] sum = new int[maxLen + 1];

            if (arr1.Length > arr2.Length)
            {
                for (int i = 0; i < maxLen; i++)
                {
                    if (i < arr2.Length)
                    {
                        tempArr[i] = arr2[i];
                    }
                    else
                    {
                        tempArr[i] = 0;
                    }
                }

                for (int i = 0; i < sum.Length; i++)
                {
                    if (i < arr1.Length)
                    {
                        sum[i] = (arr1[i] + tempArr[i]) % 10;
                    }
                    if (i > 0 && arr1[i - 1] + tempArr[i - 1] >= 10)
                    {
                        sum[i] += 1;
                    }
                }
            }
            else
            {
                for (int i = 0; i < maxLen; i++)
                {
                    if (i < arr1.Length)
                    {
                        tempArr[i] = arr1[i];
                    }
                    else
                    {
                        tempArr[i] = 0;
                    }
                }

                for (int i = 0; i < sum.Length; i++)
                {
                    if (i < arr2.Length)
                    {
                        sum[i] = (arr2[i] + tempArr[i]) % 10;
                    }
                    if (i > 0 && arr2[i - 1] + tempArr[i - 1] >= 10)
                    {
                        sum[i] += 1;
                    }
                }
            }

            return sum;
        }

        public static void Main()
        {
            while (true)
            {

                Console.Write("Insert value[0, 100] : ");
                int n = int.Parse(Console.ReadLine());

                int[] answer = new int[n * n + 1]; // +1 for n = 0
                answer[0] = 1;

                for (int i = 2; i <= n; i++) // 0 and 1 ! are 1
                {
                    answer = NumberMultiplyer(answer, i);
                }

                string final = "";
                for (int i = 0; i < answer.Length; i++)
                {
                    final = answer[i] + final;
                }

                BigInteger finalResult = BigInteger.Parse(final);

                Console.WriteLine("My result: \t" + finalResult);


                // check

                BigInteger factoriel = 1;

                int m = 1;

                while (m <= n)
                {
                    factoriel = factoriel * m;
                    m++;
                }

                Console.WriteLine("{0}! = \t\t{1}", n, factoriel);
            }
        }
    }
}