using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var list = new List<temp>();

        list.Add(new temp{name = "a", age = 1});

        list.Add(new temp{name = "b", age = 2});

        int[] ageArray = new[] {1,12,13};

        var result = list.Where(x => ageArray.Contains(x.age)).ToList();

        Console.WriteLine(result.Count);

    }

}

​

public class temp{

    public string name;

    public int age;

}