C＃故障排除中最简单的LINQ

Question

I'm trying to learn a bit of LINQ but I'm having compile issues right off the bat. Is there any specific reason why this won't work?

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text;  


namespace HelloLINQ {

    class HelloLINQ
    {
        public static void Main()
        {
            Example1();
        }


        public static void Example1()
        {
            var numbers = new int[] { 1, 5, 3, 7, 3, 8, 9, 3, 6, 6, 2 };
            var under5 = from n in numbers
                         select n;
            foreach (var n in under5)
            {
                Console.WriteLine(n);
            }
        }
    } 
}  

The error is:

Could not find an implementation of the query pattern for source type 'int[]'. 'Select' not found. Are you missing a reference to 'System.Core.dll' or a using directive for 'System.Linq'?

Answer 1

Do you have a reference to System.Core in your project? Everything else is correct.

Answer 2

Well, we have an error message, carefully written by a Microsoft employee to be helpful, so let's look at it.
Could not find an implementation of the query pattern for source type 'int[]'. 'Select' not found. Are you missing a reference to 'System.Core.dll' or a using directive for 'System.Linq'?
int[] is a basic C# type. Where are the basic C# types located? System.Core. And the error mentions checking for a reference to System.Core. So, is there a reference to System.Core?
To check this:
Solution Explorer->References. In the list, do you see System.Core?
If not, weird, but it's easily addable. Right click on references, look under .NET for System.Core, add it, and voila.