C# WinApp รบกวนช่วยตรวจสอบโค้ด ให้หน่อยครับ ต้องการให้ค่า x y เป็นจะนวนเต็ม ครับ

string intTostring(int i) {
            if (i == 1)
            {
                return "";
            }
            else if (i == -1)
            {
                return "-";
            }
            else { 
            return i.ToString();
            }
        
        }
        
        private string _Equation()
        {

            string s = "";
            int a = RandomNumberGenerator.GetInt32(1, 10);
            int x = RandomNumberGenerator.GetInt32(-5, 5);
            int b = RandomNumberGenerator.GetInt32(-10, 10);
            int y = RandomNumberGenerator.GetInt32(-5, 5);
            int d = RandomNumberGenerator.GetInt32(1, 3000);

            string o = (RandomNumberGenerator.GetInt32(1, 1000) > 500) ? "+" : "-";
            string ev = "";
            String _a ,_b,_c;
            
            _a = intTostring(a);
            _b = intTostring(b);
            switch (d)
            {
                case int n when (n >= 0 && n < 1000):
                    //ax+/-b=0
                    // ev = $"{a}{x} {o} {b}{y}  = 0";
                    do
                    {
                        a = RandomNumberGenerator.GetInt32(1, 10);
                        x = RandomNumberGenerator.GetInt32(-5, 5);
                        b = RandomNumberGenerator.GetInt32(-10, 10);
                        y = RandomNumberGenerator.GetInt32(-5, 5);

                        o = (RandomNumberGenerator.GetInt32(1, 1000) > 500) ? "+" : "-";
                    } while (a * x + (o == "+" ? b * y : -b * y) != 0);
                    _a = intTostring(a);
                    _b = intTostring(b);
                    ev = $"{_a}x {o} {_b}y  = 0";
                    break;

                case int n when (n >= 1000 && n < 2000):
                    //ax+/-b=c
                    ev = $"{_a}x {o} {_b}y  = {Eval.Execute<int>($"{a}{x} {o} {b}{y}")}";
                    break;

                case int n when (n >= 2000 && n <= 3000):
                    //ax = b+/-c
                    if (o == "+")
                        ev = $"{_a}x = {_b}y {o} {Eval.Execute<int>($"{a}{x} - {b}{y}")}";
                    else
                        ev = $"{_a}x = {_b}y {o} {Eval.Execute<int>($"{b}{y} - {a}{x}")}";
                    break;
            }

            // Parameter: Argument Position
  
            s = ev;




             a = RandomNumberGenerator.GetInt32(1, 10);
             b = RandomNumberGenerator.GetInt32(-10, 10);
             d = RandomNumberGenerator.GetInt32(1, 3000);

             o = (RandomNumberGenerator.GetInt32(1, 1000) > 500) ? "+" : "-";
            _a = intTostring(a);
            _b = intTostring(b);
            switch (d)
            {
                case int n when (n >= 0 && n < 1000):
                    //ax+/-b=0

                    do
                    {
                        a = RandomNumberGenerator.GetInt32(1, 10);
                        x = RandomNumberGenerator.GetInt32(-5, 5);
                        b = RandomNumberGenerator.GetInt32(-10, 10);
                        y = RandomNumberGenerator.GetInt32(-5, 5);

                        o = (RandomNumberGenerator.GetInt32(1, 1000) > 500) ? "+" : "-";
                    } while (a * x + (o == "+" ? b * y : -b * y) != 0);
                    _a = intTostring(a);
                    _b = intTostring(b);
                    ev = $"{_a}x {o} {_b}y  = 0";
                    break;

                case int n when (n >= 1000 && n < 2000):
                    //ax+/-b=c
                    ev = $"{_a}x {o} {_b}y  = {Eval.Execute<int>($"{a}{x} {o} {b}{y}")}";
                    break;

                case int n when (n >= 2000 && n <= 3000):
                    //ax = b+/-c
                    if (o == "+")
                        ev = $"{_a}x = {_b}y {o} {Eval.Execute<int>($"{a}{x} - {b}{y}")}";
                    else
                        ev = $"{_a}x =  {_b} y {o} {Eval.Execute<int>($"{b}{y} - {a}{x}")}";
                    break;
            }

            // Parameter: Argument Position
            return $"{s} and {ev}".Replace("--", "+").Replace("+-", "-").Replace("-+", "-")
                .Replace("- -", "+").Replace("+ -", "-").Replace("- +", "-");



        }