enum orientation : byte
   {
      north = 1,
      south = 2,
      east = 3,
      west = 4
   }

   struct route
   {
      public orientation direction;
      public double distance;
   }

   class Program
   {
      static void Main(string[] args)
      {
         route myRoute;
         int myDirection = -1;
         double myDistance;
         Console.WriteLine("1) North\n2) South\n3) East\n4) West");
         do
         {
            Console.WriteLine("Select a direction:");
            myDirection = Convert.ToInt32(Console.ReadLine());
         }
         while ((myDirection < 1) || (myDirection > 4));
         Console.WriteLine("Input a distance:");
         myDistance = Convert.ToDouble(Console.ReadLine());
         myRoute.direction = (orientation)myDirection;
         myRoute.distance = myDistance;
         Console.WriteLine("myRoute specifies a direction of {0} and a " +
            "distance of {1}", myRoute.direction, myRoute.distance);
         Console.ReadKey();
      }
红色一句中为什么myDirection不是大于1和小于4 ？

因为这是一个让你输入在他指定的范围内才往下执行。你输入不在他的枚举值之内为一个不合法的输入，让输入的人员继续输入.

看你需求了，你如果要在大于1和小于4中继续循环的话，就改不过要改成&&。