Need Help - Factoring & Prime Finding Code

Hello, I'm working on a project that outputs the numbers 2 – 100.

Next to each number, it should list all the** factors **for that number.

If the number has no factors, it should print** prime**.

**Ex.**

2 prime

3 prime

4 2

5 prime

Having some difficulty so far. I'm aware I need to use loops, but I'm not sure what to %, and by what to determine if it's a factor.

This is my fail code so far: (I realize its horrible and is incomplete)

Code :

public class Prime
{
public static void main(String[] args)
{
findPrime(factors());
factors();
}
public static void findPrime(int k)
{
int i = 2;
int ans = i%k;
while(i<=100)
{
System.out.println(ans);
i++;
}
}
public static int factors()
{
int k = 1;
for(k = 1; k <=100; k++)
{
}
return k;
}
}

Any help whatsoever is greatly appreciated. Thanks!

Re: Need Help - Factoring & Prime Finding Code

mmm... prime numbers :(

The easiest way to do this is probably seeing if for some number 1<n<101, printing out any numbers that n%i == 0 (where i is a number from 2 to n-1). If nothing was printed out, then print out prime. You can keep track of nothing being printed out by having a boolean flag to denote the primality of the number.

Code :

for (int n = 2; n <= 100; n++)
{
boolean isPrime = true; // assume n is prime
System.out.print(n + " : ");
for(int i = 2; i < n; i++)
{
if (n%i == 0)
{
System.out.print(i);
isPrime = false;
}
}
if (isPrime)
{
System.out.println("Prime");
}
else
{
System.out.println(""); // go to next line
}

Re: Need Help - Factoring & Prime Finding Code

Thanks alot! That helped me so much, I appreciate it, however, I need to work on the factoring part now, with that current code, it is printing some pretty strange numbers next to the non-prime numbers.

Ex.
Quote:

27 : 39

28 : 24714

29 : Prime

30 : 23561015

31 : Prime

32 : 24816

33 : 311

34 : 217

35 : 57

36 : 234691218

37 : Prime

Re: Need Help - Factoring & Prime Finding Code

ahh, forgot... it's not printing out any spaces between the numbers :P

Re: Need Help - Factoring & Prime Finding Code

Oh! haha I didn't realize those were factors! Thanks again!

Re: Need Help - Factoring & Prime Finding Code

lol nice one helloworld, always leave something out to confuse them. If it's solved coud you please mark it as so.

Thanks,

Chris