using System;

using System.Collections.Generic;

​

class Program

{

    static void Main()

{

    List<int> NumbersAllowed = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

​

    // Simulate pressing Enter in DotNetFiddle

    string UserInput = ""; 

​

    if (string.IsNullOrWhiteSpace(UserInput))

    {

        UserInput = Autopilot(NumbersAllowed);

        Console.WriteLine("Autopilot selected: " + UserInput);

    }

    else

    {

        Console.WriteLine("You entered: " + UserInput);

    }

}

​

​

    static string Autopilot(List<int> NumbersAllowed)

    {

        Random rand = new Random();

        int numberOfNumbersUsed = rand.Next(2, 6); // 2 to 5 inclusive

        List<string> operators = new List<string> { "+", "-", "*", "/" };

        List<int> availableNumbers = new List<int>(NumbersAllowed);

        List<string> num = new List<string>();

        List<string> op = new List<string>();

​

        for (int i = 0; i < numberOfNumbersUsed; i++)

        {

            int index = rand.Next(availableNumbers.Count);

            num.Add(availableNumbers[index].ToString());

            availableNumbers.RemoveAt(index);

        }

​

        for (int i = 0; i < numberOfNumbersUsed - 1; i++)

        {

            int index = rand.Next(operators.Count);

            op.Add(operators[index]);

        }

​

        string expression = num[0];

        for (int i = 0; i < op.Count; i++)

        {

            expression += " " + op[i] + " " + num[i + 1];

        }

​

        return expression;

    }

}

​