using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        // Get the count

        var count = Count(1,10);

        // Iterate the results

        foreach(var x in count)

        {

            Console.WriteLine(x);

        }

    }

    public static IEnumerable<int> Count(int start, int count)

    {

        // The exception will throw when the method is called, not when the result is iterated

        if (count < 0)

            throw new ArgumentOutOfRangeException(nameof(count));

        return CountCore(start, count);

    }

    private static IEnumerable<int> CountCore(int start, int count)

    {

        // If the exception was thrown here it would be raised during the first MoveNext()

        // call on the IEnumerator, potentially at a point in the code far away from where

        // an incorrect value was passed.

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

        {

            yield return start + i;

        }

    }

}