07. Primes in Given Range

using System;
using System.Collections.Generic;
using System.Numerics;
using System.Text;

namespace CSharpDemos
{
    class Program
    {
        static void Main(string[] args)
        {
            int startNum = int.Parse(Console.ReadLine());
            int endNum = int.Parse(Console.ReadLine());

            if (startNum > endNum)
            {
                Console.WriteLine("(empty list)");
            }

            List<int> primes = new List<int>(PrimesInRange(startNum, endNum));

            string result = string.Join(", ", primes);

            Console.WriteLine(result);
        }

        static List<int> PrimesInRange(int startNum, int endNum)
        {
            List<int> result = new List<int>();

            for (int i = startNum; i <= endNum; i++)
            {
                if (i < 2)
                {
                    continue;
                }
                bool isPrime = true;
                for (int j = 2; j <= Math.Sqrt(i); j++)
                {
                    if (i % j == 0)
                    {
                        isPrime = false;
                        break;
                    }

                }
                if (isPrime)
                {
                    result.Add(i);
                }
            }
            return result;
        }
    }
}