问有没有办法在c#中生成随机数学表达式？

EN

using System;
using System.Text;

public class Test
{
    public static void Main()
    {
        Random r = new Random();
        StringBuilder builder= new StringBuilder();


        int numOfOperand = r.Next(1, 20); // it is just a test so I just want to have up to 20 operands.
        int randomNumber;
        for(int i = 0 ; i<numOfOperand ; i++){

            randomNumber = r.Next(1, 1000);
            builder.Append(randomNumber);


            int randomOperand = r.Next(1, 4);

            string operand = null;

            switch (randomOperand)
            {
                case 1:
                    operand = "+";
                break;
                case 2:
                    operand = "-";
                break;
                case 3:
                    operand = "*";
                break;
                case 4:
                    operand = "/";
                break;
            }
            builder.Append(operand);
        }
        randomNumber = r.Next(1, 1000);
            builder.Append(randomNumber);

        Console.WriteLine(builder.ToString());
    }
}