Program.cs
 

using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int time = 20;
      if (time < 18) 
      {
        Console.WriteLine("Good day.");
      } 
      else 
      {
        Console.WriteLine("Good evening.");
      }
    }
  }
}

Result:
Good evening.