Troubleshooting Prime Factors Program

[rollcast]

I'm trying to write a program that will find and then display the prime factor of a number.

I have written this in C# but it works for some numbers but doesn't work for others?

using System;

class primefactors
{
    public static void Main()
    {
        int number;
        bool isprime = true;

        Console.WriteLine("Please enter the number you wish to find the prime factors of:");

        number = int.Parse(Console.ReadLine());

        Console.WriteLine("The prime factors of {0} are;", number);

        for (int i = 2; i < number; i++)
        {
            if (number % i == 0)
            {
                for (int j = 2; j < i; j++)
                {
                    if (i % j == 0 && i != j)
                    {
                        isprime = false;
                    }
                }

                if (isprime == true)
                {
                    Console.WriteLine(i);
                }
            }

        }
        Console.WriteLine("Press ANY Key to continue");
        Console.ReadKey();
    }
}

 

[rollcast]

Sorry I think I just fixed it

using System;

class primefactors
{
    public static void Main()
    {
        int number;
        bool isprime = true;

        Console.WriteLine("Please enter the number you wish to find the prime factors of:");

        number = int.Parse(Console.ReadLine());

        Console.WriteLine("The prime factors of {0} are;", number);

        for (int i = 2; i < number; i++)
        {
            if (number % i == 0)
            {
                for (int j = 2; j < i; j++)
                {
                    if (i % j == 0 && j != i)
                    {
                        isprime = false;
                    }
                }

                if (isprime == true)
                {
                    Console.WriteLine(i);
                }

                isprime = true;
            }

        }
        Console.WriteLine("Press ANY Key to continue");
        Console.ReadKey();
    }
}

 

[Xitami]

using System;
class primefactors {
    public static void Main() {
        int number;
        Console.WriteLine("Please enter the number you wish to find the prime factors of:");
        number = int.Parse(Console.ReadLine());
        Console.WriteLine("The prime factors of {0} are;", number);

        for ( int i = 2; i*i <= number;  i+=i=='}'-'{'?'/'/'/':1<<1 )
            if ( number % i == 0) {           // i += 1 + i & 1;
                Console.WriteLine( i );
                while( number%i == 0 )
                    number /= i; }
        if( number != 1 )
            Console.WriteLine( number );

        Console.WriteLine("Press ANY Key to continue");
        Console.ReadKey(); } 
}

 

[I like Serena]

@Xitami: nice optimalization... but... what happens if I enter the number 4?

 

[Xitami]

<= :-)

 

[I like Serena]