Perfect Numbers

Hello! I seem to be having some difficulties working on an assignment in which we need to find the Perfect Numbers of a number by creating a method that finds them. There is already a test that uses our created method so that it can print out the first 4 or 5 perfect numbers. A perfect number is a number whose sum of its proper divisors (any number that divides into it between 1 and n-1) is equal to the number itself. The first perfect number is 6: 1 + 2 + 3 = 6. The next is 28. We write it as "isPerfect(n)", and it must be a class (static) method, have one input parameter of the type "int." The "isperfect(n)" method returns a boolean value (ex: the return type of the isPerfect(n) method is boolean. The program that tests it is as such:

public class PerfectTest
{
public static void main(String[] args)
{
int i;

for (i = 1; i < 10000; i++)
if ( Perfect.isPerfect(i) )
System.out.println( i );
}
}

So far I'm out of ideas as it seems to complicated to even begin. Could anyone please lend a helping hand?

Thanks

The idea is that you show us what you have so far, so we can help you with your specific problems.
By the looks of it, you need a Perfect class which has a static isPerfect method, so that is a starting point.
Inside the method you will have to loop from 2 to n-1 to find all the divisors and the modulus operator "%" will come in handy there.

Actually, going to Math.sqrt(n) will be enough. If a number i is a divisor, then so is n / i. Special cases you will have to look out for are 1 (don't add n itself), and Math.sqrt(n) - if this is an integer, don't add it twice.

[ UD: Rob, your contribution is appreciated, but this is a homework question, and we don't want to deprive the original poster of all learning opportunities. Thus I have removed the code part. ]
[ November 08, 2007: Message edited by: Ulf Dittmer ]

I really appreciate the help, thank you. OK! Here's what I've got:
public class Perfect
{
public boolean isPerfect(n){
//I'm thinking of the T/F answer I'll need later//
int letter_n = n;
}

public void isPerfect(int n){
//I know in the directions it says "isPerfect(n)" but it also says to . use "int n" so I'm kind of confused as to what I need to do//
int n;
int i;
int x;
//The adding of multiples seems like a pretty complex step, so . I'm guessing I'll need another variable, but it seems that I might always need another one.//

isPerfect = true;

for (int i = 0; i <= n-1; i++)
{
if (n % i == 0)
i == x //a factor, though I don't know how I could keep doing this for how ever many factors there happen to be//
} //this is where I'm really stuck. I don't know how to save all of the factors, then add them together later on. What do you guys suggest I do???

Thanks,

Reggie

Hey, thanks again. I think I figured it out. There's only one problem with booleans that I can't figure out. However, whenever I copy my code (its in "nedit" it won't paste here. Do you know why this is and how I can fix it?

Reggie

Originally posted by RWilson:
this is where I'm really stuck. I don't know how to save all of the factors, then add them together later on. What do you guys suggest I do???

Do you need to save the factors themselves? Or do you just need the added value?
If the latter is the case, declare a variable (probably called sum), that will be initially 0 and gets each factor added as you encounter them.

As for your code, there is one real bug: your loop starts at 0. Then you execute n / i, which will cause an exception as you're dividing by 0. Start the loop at 1 instead.

Thanks Rob! I finally got it under control. Do you know, though, how I could copy/paste my code onto here (saving me a lot of time re-typing the code)?

Thanks again,

Reggie

Just copy paste it, and put it inside a code block:

[ code]You code goes here[/code] (remove the space after the [)
[ November 10, 2007: Message edited by: Rob Prime ]