c# - 有人可以解释为什么会计算一个更高和更低的数字但我的实际数字不会吗？

Question

所以，这个控制台应用程序只打印一个数字是否是素数，几乎适用于每个数字，但是当要求分配使用两个硬编码数字（7389274937501454911 和 9389274937501454911）对函数进行时间测试时，这些数字不会打印出任何东西但是两个数字的 +1 或 -1 将打印出来。

using System;

namespace IsPrime
{
    class MainClass
    {
        public static void Main (string[] args)
        {
            string isPlaying = "y";
            bool isPrime;

            while(isPlaying == "y")
            {
                var timer = System.Diagnostics.Stopwatch.StartNew ();
                isPrime = isPrimeNum(9389274937501454911);
                if (isPrime)
                {
                    Console.WriteLine(9389274937501454911 + " is Prime");
                }
                else 
                    Console.WriteLine(9389274937501454911 + " is not prime");

                isPrime = isPrimeNum(7389274937501454911);
                if (isPrime)
                {
                    Console.WriteLine(7389274937501454911 + " is Prime");
                }
                else 
                    Console.WriteLine(7389274937501454911 + " is not prime");
                timer.Stop ();
                var time = timer.ElapsedMilliseconds;
                Console.WriteLine("Elasped Time: " + time + "\n");

                Console.WriteLine("Do you want to play again?: y / n");
                isPlaying = Console.ReadLine ();

            }
        }

        static bool isPrimeNum(ulong n)
        {
            if (n == 1 || n == 2)
                return true;

            if (n % 2 == 0)
                return false;

            for(ulong i = 3; i < n; i = i + 2) 
            {
                if (n % i == 0)
                    return false;
            }

            return true;
        }

    }
}

Answer 1

我已经修改了你的代码，现在试试

using System;

namespace IsPrime
{
    class MainClass
    {
        public static void Main (string[] args)
        {
            string isPlaying = "y";
            bool isPrime;

            while(isPlaying == "y")
            {
                var timer = System.Diagnostics.Stopwatch.StartNew ();
                isPrime = IsPrime(9389274937501454911);
                if (isPrime)
                {
                    Console.WriteLine(9389274937501454911 + " is Prime");
                }
                else 
                    Console.WriteLine(9389274937501454911 + " is not prime");

                isPrime = IsPrime(7389274937501454911);
                if (isPrime)
                {
                    Console.WriteLine(7389274937501454911 + " is Prime");
                }
                else 
                    Console.WriteLine(7389274937501454911 + " is not prime");
                timer.Stop ();
                var time = timer.ElapsedMilliseconds;
                Console.WriteLine("Elasped Time: " + time + "\n");

                Console.WriteLine("Do you want to play again?: y / n");
                isPlaying = Console.ReadLine ();

            }
        }

        public static bool IsPrime(ulong number)
        {
            if (number == 1) return false;
            if (number == 2) return true;
            if (number % 2 == 0) return false;

           //This returns the whole number greater than or equal to the specified number, and in this case
           //In this case, I take the square root, obvious to divide in half, so the variable i increases twice, since I'm working with the biggest number and divided in half
            var boundary = (ulong)Math.Floor(Math.Sqrt(number));

            for (ulong i = 3; i <= boundary; i += 2)
            {
                if (number % i == 0) return false;
            }

            return true;
        }
    }
}