Gen v.3.0

using Newtonsoft.Json;
using System;
using System.Threading;


namespace serialize
{


    class Generator
    {


        public (int, int, int, int) GetMod(int diff)
        {
            int mod1 = 1;// +-
            int mod2 = 1;// +-
            int mod3 = 1;// */
            int mod4 = 1;// */

            if (diff == 0)//только сумма
            {
                mod1 = 9;
                mod2 = 9;
            }
            if (diff == 1)// сумма & разность
            {
                mod1 = 11;
                mod2 = 11;
            }
            if (diff == 2)// сумма & разность & произведение
            {
                mod1 = 10;// +-
                mod2 = 10;// +-
                mod3 = 9;// */
                mod4 = 9;// */
            }
            if (diff == 3)// сумма & разность & произведение
            {
                mod1 = 19;// +-
                mod2 = 19;// +-
                mod3 = 9;// */
                mod4 = 9;// */
            }
            if (diff > 3)
            {
                mod1 = 20 + (diff - 2) * (diff - 2);
                mod2 = 20 + (diff - 2) * (diff - 2);
                mod3 = 10 + (diff - 2) * 2;
                mod4 = 10 + (diff - 2) * 2;
            }

            return (mod1, mod2, mod3, mod4);
        }

        public static char GetSign(int diff = 0)
        {

            Random rnd = new Random();
            int l = rnd.Next();
            Thread.Sleep(5);
            int r = rnd.Next();
            int tmp = rnd.Next(Math.Min(l, r), Math.Max(l, r)) % 4;
            char result = '.';
            if (diff == 0)
            {
                tmp = 0;
            }

            if (diff == 1)
            {
                while (tmp > 1)
                { tmp = rnd.Next() % 4; }
            }
            if (diff == 2)
            {
                while (tmp > 2)
                { tmp = rnd.Next() % 4; }
            }

            switch (tmp)
            {
                case (0):
                    result = '+';
                    break;
                case (1):
                    result = '-';
                    break;
                case (2):
                    result = '*';
                    break;
                case (3):
                    result = '/';
                    break;
                default:
                    break;
            }
            return result;
        }

        public (int, int) GetPair(int mod1, int mod2)
        {

            Random rnd = new Random();
            int res1, res2;
            res1 = (rnd.Next() % mod1) + 1;
            Thread.Sleep(10);
            res2 = (rnd.Next() % mod2) + 1;
            return (res1, res2);
        }



        public (string, char, string, int) Build(char Sign, int diff)
        // first sign second result
        {
            (string, char, string, int) result;
            result.Item1 = "";
            result.Item2 = '.';
            result.Item3 = "";
            result.Item4 = 0;

            var MOD = GetMod(diff);

            if (Sign == '+')
            {
                do
                {
                    (int, int) Expression = GetPair(MOD.Item1, MOD.Item2);
                    result.Item1 = Expression.Item1.ToString();
                    result.Item2 = Sign;
                    result.Item3 = Expression.Item2.ToString();
                    result.Item4 = Expression.Item1 + Expression.Item2;
                } while (diff > 2 && result.Item4 < (diff - 1) * 10);
            }
            else
            if (Sign == '-')
            {
                (int, int) Expression;
                do
                {
                    Expression = GetPair(MOD.Item1, MOD.Item2);
                    if (Expression.Item1 < Expression.Item2)
                    {
                        int a = Expression.Item1;
                        Expression.Item1 = Expression.Item2;
                        Expression.Item2 = a;
                    }
                } while (diff > 1 && Expression.Item1 < 3 * (diff));

                result.Item1 = Expression.Item1.ToString();
                result.Item2 = Sign;
                result.Item3 = Expression.Item2.ToString();
                result.Item4 = Expression.Item1 - Expression.Item2;

            }
            else
            if (Sign == '/')
            {
                (int, int) Expression = GetPair(MOD.Item3, MOD.Item4);
                Expression.Item1 = Expression.Item2 * Expression.Item1;
                result.Item1 = Expression.Item1.ToString();
                result.Item2 = Sign;
                result.Item3 = Expression.Item2.ToString();
                result.Item4 = Expression.Item1 / Expression.Item2;
            }
            else
            {
                (int, int) Expression = GetPair(MOD.Item3, MOD.Item4);
                if (Expression.Item1 == 1)
                    Expression.Item1++;
                if (Expression.Item2 == 1)
                    Expression.Item2++;
                result.Item1 = Expression.Item1.ToString();
                result.Item2 = Sign;
                result.Item3 = Expression.Item2.ToString();
                result.Item4 = Expression.Item1 * Expression.Item2;
            }

            return result;
        }


        static void Main(string[] args)
        {
            int diff = 8;
            Generator abs = new Generator();
            //for (diff = 0; diff < 10; ++diff)
            {
                Console.WriteLine();
                Console.WriteLine();
                for (int i = 0; i < 10; ++i)
                {

                    var a = abs.Build(GetSign(diff), diff);
                    Thread.Sleep(100);


                    Console.WriteLine(a);




                }

            }
        }

    }
}