using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var listNumbers = Enumerable.Range(1, 100);

        var groupedByUnits = listNumbers.GroupBy(n => n % 10);

        foreach (var group in groupedByUnits)

        {

            Console.WriteLine($"---------{group.Key}------------");

            foreach (var num in group)

                Console.WriteLine(num);

        }

    }

}