Controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SudokuLibrary
{
    public class Controller
    {
        private const int Length = 9;
        private int[,] arr;

        public int[,] Array
        {
            get
            {
                if (arr == null)
                    arr = new int[Length, Length];
                return arr;
            }
        }

        public bool CheckCell(int i, int j, int num)
        {
            // if this numer was found returns false and whole function returns false
            if (CheckSquare(i, j, num) == false )
                return false;

            // if this numer was found returns false and whole function returns false
            if (CheckRow(i, num) == false)
                return false;

            // if this numer was found returns false and whole function returns false
            if (CheckColumn(j, num) == false)
                return false;

            // otherwise returns true
            return true;
        }

        /// <summary>
        /// returns true if no num in square around was found. Otherwise returns false
        /// </summary>
        /// <param name="i">x coordinate of input </param>
        /// <param name="j">y coordinate of input</param>
        /// <param name="num">the numer of input </param>
        /// <returns></returns>
        private bool CheckSquare(int i, int j, int num)
        {
            for (int x = i/3; x < i / 3 + 1; x++)
            {
                for (int y = j/3; y < 3 + 1; y++)
                {
                    if (arr[x, y] == num)
                        return false;
                }
            }

            return true;
        }

        /// <summary>
        /// returns true if no num was found in row. Otherwise false
        /// </summary>
        /// <param name="i"></param>
        /// <param name="num"></param>
        /// <returns></returns>
        private bool CheckRow(int i, int num)
        {
            for (int y = 0; y < Length; y++)
            {
                if (arr[i,y] == num)
                    return false;
            }

            return true;
        }

        /// <summary>
        /// returns true if no num was found in column. Otherwise false
        /// </summary>
        /// <param name="j"></param>
        /// <param name="num"></param>
        /// <returns></returns>
        private bool CheckColumn(int j, int num)
        {
            for (int x = 0; x < Length; x++)
            {
                if (arr[x,j] == num)
                    return false;
            }

            return true;
        }
    }
}