Store the outcome of an algorithm that looks for prime numbers in a file (C#)

Question

I am trying to make a program that looks for prime numbers, displays them in the console and stores the numbers in a file. The program already stores the numbers in a file, but it doesn't display the numberrs in the console. Here is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace Priemgetallen
{
    class Program
    {
    static void Main()
    {
        using (StreamWriter writer = new StreamWriter("C://Users//mens//Documents//PriemGetallen.txt"))
        {
            Console.SetOut(writer);
            Act();
        }
    }

    static void Act()
    {

        double maxGetal = double.MaxValue;
        Console.WriteLine("--- Primes between 0 and 100 ---");
        for (int i = 0; i < maxGetal; i++)
        {
            bool prime = PrimeTool.IsPrime(i);
            if (prime)
            {
                Console.Write("Prime: ");
                Console.WriteLine(i);
            }
        }
    }

    public static class PrimeTool
    {
        public static bool IsPrime(int candidate)
        {
            // Test whether the parameter is a prime number.
            if ((candidate & 1) == 0)
            {
                if (candidate == 2)
                {
                    return true;
                }
                else
                {
                    return false;
                }
            }
            // Note:
            // ... This version was changed to test the square.
            // ... Original version tested against the square root.
            // ... Also we exclude 1 at the end.
            for (int i = 3; (i * i) <= candidate; i += 2)
            {
                if ((candidate % i) == 0)
                {
                    return false;
                }
            }
            return candidate != 1;
        }
    }

}

}

Answer 1

That's because of the line Console.SetOut(writer);. You are sending console output to the file.

Rather than do it the way you are, ditch the StreamWriter and instead use:

if (prime)
{
    var primeText = string.Format("Prime: {0}", i);
    Console.WriteLine(primeText );
    File.AppendAllText(@"C:\Users\mens\Documents\PriemGetallen.txt",
                       primeText + Environment.NewLine);
}