Write a program in C# to find the largest prime among a collection of numbers

Let's say that we have a collection of integers as {104723, 104729, 9998,448 }. Objective is to find the largest prime among a collection of numbers. The below program will do so

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var numberCollection = new List<int>() {104723, 104729, 9998,448 };
            var nonPrimeCollection = new List<int>();

            for (int j = 0; j < numberCollection.Count; j++)
            {
                for (int i = 2; i < numberCollection[j]; i++)
                {
                    if (numberCollection[j] % i == 0)
                    {                       
                        nonPrimeCollection.Add(numberCollection[j]);
                        break;
                    }
                }                
            }
            Console.WriteLine("Largest Prime {0} ", numberCollection.Except(nonPrimeCollection).Max());
            Console.ReadKey();
        }
    }
}


Result
--------
Largest Prime 104729

The outer for loop is looping thru the entire collection. The inner for loop starts at 2 and picks up those elements that are not primes. And then we are finding the numbers which are prime and finally finding the max.