Program

using System;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            DirectoryInfo d = new DirectoryInfo("mydir");

            if(d.Exists)
                Console.WriteLine("Directory exists");
            else
                Console.WriteLine("Directory does not exists");
        }
    }
}

Output

Directory exists

In this program, we create an object of DirectoryInfo class and initialize with a directory-name, then check directory exists or not using Exists property of DirectoryInfo class.

Note: In above program, we need to remember, when we use "DirectoryInfo" class, System.IO namespace must be included in the program.