using System;

using System.Linq;

​

namespace Cli2

{

    public static class Program

    {

        public static void Main(string[] args)

        {

            var table = new[]

            {

                new[] {" ", "0", "1", "2"},

                new[] {"A", null, null, null},

                new[] {"B", null, null, null},

                new[] {"C", null, null, null},

            };

​

            var rows = table.Length;

            var cols = table.First().Length;

            var header = $"┌{string.Join("", Enumerable.Repeat("──┬", cols - 1))}──┐";

            var middle = $"├{string.Join("", Enumerable.Repeat("──┼", cols - 1))}──┤";

            var footer = $"└{string.Join("", Enumerable.Repeat("──┴", cols - 1))}──┘";

​

            Console.WriteLine(header);

            for (var i = 0; i < rows; ++i)

            {

                foreach (var cell in table[i])

                    Console.Write($"│ {cell ?? " "}");

                Console.WriteLine("│");

                if (i < rows - 1)

                    Console.WriteLine(middle);

            }

            Console.WriteLine(footer);

​

        }

    }

}