Practice Exercise to solve

using System;

namespace RightAngleConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Please enter the number of rows you want to print..");
            int rows = int.Parse(Console.ReadLine());
            Console.WriteLine("Below is the result:\n");
            for (var i = 1; i <= rows; i++)
            {
                for (var j = 1; j <= i; j++)
                    Console.Write(j);
                Console.WriteLine();
            }
            Console.ReadKey();
        }
    }
}

http://www.w3resource.com/csharp-exercises/for-loop/csharp-for-loop-exercise-9.php