CODEWITHSUNDEEP
c#
isakN
isakN

Reputation: 9

Program to find perfect numbers

I'm trying to create a program that will find the first five perfect numbers. It almost works but for some reason the numbers 24 and 2016 also get mixed in. I have no idea why. Heres the code:

    int perfectNums, amount = 5, tries;
    bool check;

    public void Run()
    {
        perfectNums = 0;
        
        for (int i = 1; perfectNums < amount; i++)
        {
            check = isPerfectNum(i);

            if (check == true)
            {
                perfectNums++;
                Console.WriteLine(i);
            }
        }

    }

    public static bool isPerfectNum(int num)
    {
        bool isPerfect = false;
        int sum = 0;

        for (int i = 1; i < num; i++)
        {
            if (num % i == 0)
            {
                sum = sum + i;
            }

            if (sum == num)
            {
                isPerfect = true;
                
            }
        }


        return isPerfect;
    }
}

}

Upvotes: 0

Views: 300

Answers (2)

Marc Gravell
Marc Gravell

Reputation: 1063499

You can't deduce whether it is a perfect number until you have finished calculating the aliquot sum;

For example:

    public static bool IsPerfectNum(int num)
    {
        int aliquotSum = 0;

        for (int i = 1; i < num; i++)
        {
            if (num % i == 0)
            {   // is a divisor
                aliquotSum += i;
            }
        }

        return aliquotSum == num;
    }

(you could also probably half the number of tests - there won't be any divisors above num/2)

Upvotes: 1

Giacomo Pirinoli
Giacomo Pirinoli

Reputation: 568

The check:

if (sum == num)
{
  isPerfect = true;       
}

should be outside the loop, at the bottom of your method; otherwise at a certain iteration you would get 1+2+3+4+6+8=24 but you are still processing, and the final check would have been 1+2+3+4+6+8+12!=24. Btw, I agree to just debug your code step by step in order to get the faulty part.

Upvotes: 0

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