Prime Factors In C#

I want to c开发者_如何学运维reate a program in C# 2005 which calculates prime factors of a given input. i want to use the basic and simplest things, no need to create a method for it nor array things etc. just simple modulus. is there any code which fulfills what i desire?

here is the code for finding simple factors, i need this code to be modified to calculate prime factors

class Program
{
    static void Main(string[] args)
    {
        int a, b;
        Console.WriteLine("Please enter your integer: ");
        a = int.Parse(Console.ReadLine());
        for (b = 1; b <= a; b++)
        {
            if (a % b == 0)
            {
                Console.WriteLine(b + " is a factor of " + a);
            }
        }
        Console.ReadLine();



    }
}

int a, b;
Console.WriteLine("Please enter your integer: ");
a = int.Parse(Console.ReadLine());

for (b = 2; a > 1; b++)
    if (a % b == 0)
    {
        int x = 0;
        while (a % b == 0)
        {
            a /= b;
            x++;
        }
        Console.WriteLine($"{b} is a prime factor {x} times!");
    }
Console.WriteLine("Th-Th-Th-Th-Th-... That's all, folks!");

public static List<int> Generate(int number)
{
    var primes = new List<int>();

    for (int div = 2; div <= number; div++)
        while (number % div == 0)
        {
            primes.Add(div);
            number = number / div;
        }
    
    return primes;
}

If you want to learn steps of development you can watch video here.

You can go one better as the divisor can never be larger than the square root of the number.

 for(int div = 2; div <= Math.Sqrt(number); div++)

Try this code (I incorporated various solutions in this code). Although, interpolation is not in 2005 (I think so....)

So, anyways, try this:

// C# Program to print all prime factors 
using System; 

namespace prime
{
    public class Prime
    { 

        public static void PrimeFactors(int n)
        {
            Console.Write($"Prime Factors of {n} are:  ");

            // Prints all the numbers of 2  
            while (n % 2 == 0)
            {
                Console.Write("2 ");
                n /= 2;
            }

            // As no 2 can be further divided, this probably means that n
            // is now an odd number
            for(int i = 3; i <= Math.Sqrt(n); i += 2)
            {
                while (n % i == 0)
                {
                    Console.Write($"{i} ");
                    n /= i;
                }
            }

            // This is for case if n is greater than 2
            if (n > 2)
            {
                Console.Write($"{n} ");
            }

        }

        // Prompts user to give Input to number and passes it on 
        // the PrimeFactors function after checking its format
        public static void RunPrimeFactors()
        {
            Console.Write("Enter a number: ");
            if (int.TryParse(Console.ReadLine(), out int n))
            {
                PrimeFactors(n);
            }
            else
            {
                Console.WriteLine("You entered the wrong format");
            }

        }
        // Driver Code 
        public static void Main()
        {
            RunPrimeFactors();
        }

    }
}

This version lists all the factors as an explicit formula:

static void Main(string[] args)
    {
        Console.WriteLine("Please enter your integer (0 to stop): ");

        int a = int.Parse(Console.ReadLine());
        while(a>0)
        {
            List<int> primeFactors = PrimeFactors(a);
            LogFactorList(primeFactors);
            a = int.Parse(Console.ReadLine());
        }
        Console.WriteLine("Goodbye.");
    }


    /// <summary>
    /// Find prime factors
    /// </summary>
    public static List<int> PrimeFactors(int a)
    {
        List<int> retval = new List<int>();
        for (int b = 2; a > 1; b++)
        {               
            while (a % b == 0)
            {
                a /= b;
                retval.Add(b);
            }               
        }
        return retval;
    }

    /// <summary>
    /// Output factor list to console
    /// </summary>
    private static void LogFactorList(List<int> factors)
    {
        if (factors.Count == 1)
        {
            Console.WriteLine("{0} is Prime", factors[0]);
        }
        else
        {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < factors.Count; ++i)
            {
                if (i > 0)
                {
                    sb.Append('*');
                }
                sb.AppendFormat("{0}", factors[i]);
            }
            Console.WriteLine(sb.ToString());
        }
    }

using static System.Console;

namespace CodeX
{
    public class Program
    {
        public static void Main(string[] args)
        {
            for (int i = 0; i < 20; i++)
            {
                if (IsPrime(i))
                {
                    Write($"{i} ");
                }
            }
        }

        private static bool IsPrime(int number)
        {
            if (number <= 1) return false;  // prime numbers are greater than 1

            for (int i = 2; i < number; i++)
            {
                // only if is not a product of two natural numbers
                if (number % i == 0)       
                    return false;
            }

            return true;
        }
    }
}