private void button1_Click(object sender, EventArgs e)
        {
            var    chisla = new Stack <double>();
            string str;

            str = textBox1.Text;
            var list = str.Split(' ');

            for (int i = 0; i < list.Length; i++)
            {
                if ((list[i] == "+") || (list[i] == "-") || (list[i] == "*") || (list[i] == "/"))
                {
                    var num2 = chisla.Get_and_Remove();
                    var num1 = chisla.Get_and_Remove();
                    switch (list[i])
                    {
                    case "+":
                        chisla.Add(num1 + num2);
                        break;

                    case "-":
                        chisla.Add(num1 - num2);
                        break;

                    case "*":
                        chisla.Add(num1 * num2);
                        break;

                    case "/":
                        chisla.Add(1.0 * (num1 / num2));
                        break;
                    }
                }
                else
                {
                    chisla.Add(double.Parse(list[i]));
                }
            }
            textBox1.Text = Convert.ToString(chisla.Get());
        }